codeforces 630F Selection of Personnel

最新推荐文章于 2016-08-08 23:15:21 发布

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本文介绍了一个具体的组合数学问题，即从n个候选人中选择5到7人的创新开发团队的所有可能组合数量。通过给出一个计算组合数C(n, i)的算法来解决该问题，避免了在大规模数据输入时出现超时的情况。

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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







#include<cstdio>
#include<cstring>
#include<iostream>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
using namespace std;
//重点在于计算C(n,i)  要防止超时

//题目大意：收到n个人的简历，要组成一个团队（人数为5或6或7）
//即  计算C(n,5)+C(n,6)+C(n,7); 
long long C(long long n,long long i)
{
	//printf("%lld %lld\n",n,i);
	long long num=1;
	long long k,j;
	for(j=n,k=1;k<=i&&j>=n-i+1;k++,j--)
	{
			num=num*j;
			num=num/k;
	}
	//printf("%lld\n",num);
	return num;
}
int main()
{
	long long  n;
	while(scanf("%lld",&n)!=EOF)
	{
		if(n==5)
		{
			printf("1\n");
		}
		else if(n==6)
		{
			printf("7\n");
		}
		else if(n==7)                                                              
		{
			printf("29\n");
		}
		else
		{
			long long i;
			long long sum=0;
			for(i=7;i>=5;i--)
			{
				sum=sum+C(n,i);
			}
			printf("%lld\n",sum);
		}
	}
	return 0;
}