codeforces 630F Selection of Personnel（组合数）

F. Selection of Personnel

time limit per test

0.5 seconds

memory limit per test

64 megabytes

input

standard input

output

standard output

One company of IT City decided to create a group of innovative developments consisting from 5 to 7 people and hire new employees for it. After placing an advertisment the company received n resumes. Now the HR department has to evaluate each possible group composition and select one of them. Your task is to count the number of variants of group composition to evaluate.

Input

The only line of the input contains one integer n (7 ≤ n ≤ 777) — the number of potential employees that sent resumes.

Output

Output one integer — the number of different variants of group composition.

Examples

input

7

output

29

题意：给一个数n（7<=n<=777）要求从这n个人中抽5到7个问总共多少种可能
题解：组合数c（n,5）+c(n,6)+c(n,7)注意防止溢出

#include<stdio.h>
#include<string.h>
#include<string>
#include<math.h>
#include<algorithm>
#define LL long long
#define PI atan(1.0)*4
#define DD double
#define MAX 10010
#define mod 100
#define dian 1.000000011
#define INF 0x3f3f3f
using namespace std;
LL solve(LL n,LL m)  
{  
    int num=1;  
    LL ans=1;  
    while(m--)  
    {  
        ans*=(n-m);  
        ans/=num;  
        num++;  
    }  
    return ans;  
}  
int main()
{
	LL n,m,j,i,x,y;
	LL sum,a,b,c,ans;
    while(scanf("%lld",&n)!=EOF)
	{	
	    sum=0;
		for(i=5;i<=7;i++)
		{
			sum+=solve(n,i);
		}
		printf("%lld
",sum);
	} 
	return 0;
}