2015 HUAS Provincial Select Contest #2 C

题目：

Description

Vanya got n cubes. He decided to build a pyramid from them. Vanya wants to build the pyramid as follows: the top level of the pyramid must consist of 1 cube, the second level must consist of 1 + 2 = 3 cubes, the third level must have 1 + 2 + 3 = 6 cubes, and so on. Thus, the i-th level of the pyramid must have 1 + 2 + ... + (i - 1) + i cubes.

Vanya wants to know what is the maximum height of the pyramid that he can make using the given cubes.

Input

The first line contains integer n (1 ≤ n ≤ 10⁴) — the number of cubes given to Vanya.

Output

Print the maximum possible height of the pyramid in the single line.

题目大意：给个金字塔形。第一层1，第二层1+2，。。。。。。，第i层1+2+。。。+i，输入N，判断它最多能积累到哪一层。

解题思路：用等差数列的求和公式(1+i)*i/2求出每行的值，再用的变量将他们的值加到一起，在与N比较，看哪个数比N大，就说明N最多在I-1行。

代码：

#include<iostream>
#include<cstdio>
using namespace std;
int main()
{
    int n,d=0,sum=0;
    while(cin>>n)
    {
        if(n>=1&&n<=10000)
        {
            int i=1;
           while(1)
           {
               sum+=(1+i)*i/2;
               if(sum>n)
               {
                   d=i-1;
                   break;
               }
               i++;
           }
           printf("%d
",d);
           d=0;
        }
    }
    return 0;
}