输入年月日判断是这一年的哪一天

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            while (true)
            {
                Console.Write("请输入年");
                int year = int.Parse(Console.ReadLine());
                Console.Write("请输入月");
                int mouth = int.Parse(Console.ReadLine());
                Console.Write("请输入日");
                int day = int.Parse(Console.ReadLine());
                if (mouth == 1 &&( year > 1795 && year < 9999) &&( day > 0 && day <= 31))
                {
                    Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", day);
                }
                else if ((year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) &&( year > 1795 && year < 9999 )&&( mouth > 0 && mouth <= 12) && (day > 0 && day <= 31))
                {
                    if (mouth == 2 && day <= 29)
                    {
                        int m = 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 3 && day <= 31)
                    {
                        int m = 31 + 29 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 4 && day <= 30)
                    {
                        int m = 31 + 29 + 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 5 && day <= 31)
                    {
                        int m = 31 + 29 + 31 + 30 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 6 && day <= 30)
                    {
                        int m = 31 + 29 + 31 + 30 + 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 7 && day <= 31)
                    {
                        int m = 31 + 29 + 31 + 30 + 31 + 30 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 8 && day <= 30)
                    {
                        int m = 31 + 29 + 31 + 30 + 31 + 30 + 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 9 && day <= 31)
                    {
                        int m = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 10 && day <= 31)
                    {
                        int m = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 11 && day <= 30)
                    {
                        int m = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 12 && day <= 31)
                    {
                        int m = 31 + 29 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                }
                else if ((year > 1795 && year < 9999) &&( mouth > 0 && mouth <= 12) && (day > 0 && day <= 31))
                {
                    if (mouth == 2 && day <= 28)
                    {
                        int m = 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 3 && day <= 31)
                    {
                        int m = 31 + 28 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 4 && day <= 30)
                    {
                        int m = 31 + 28 + 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 5 && day <= 31)
                    {
                        int m = 31 + 28 + 31 + 30 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 6 && day <= 30)
                    {
                        int m = 31 + 28 + 31 + 30 + 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 7 && day <= 31)
                    {
                        int m = 31 + 28 + 31 + 30 + 31 + 30 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 8 && day <= 30)
                    {
                        int m = 31 + 28 + 31 + 30 + 31 + 30 + 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 9 && day <= 31)
                    {
                        int m = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 10 && day <= 31)
                    {
                        int m = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 11 && day <= 30)
                    {
                        int m = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                    else if (mouth == 12 && day <= 31)
                    {
                        int m = 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + day;
                        Console.WriteLine(year.ToString() + "年" + mouth.ToString() + "月" + day.ToString() + "日" + "是这一年的第{0}天", m);
                    }
                }
                else
                {
                    Console.WriteLine("请输入正确的年月日");
                }
                Console.ReadLine();
            }
        }
    }
}