Codeforces 630F：Selection of Personnel【数列组合】

最新推荐文章于 2016-04-21 19:20:17 发布

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本文介绍了一家IT公司如何通过组合数学原理来计算不同规模团队的可能组成方式数量。通过对输入简历数目的处理，文章提供了一个实际的C++代码示例，展示了如何避免整数溢出的问题。

Selection of Personnel

Time Limit:500MS Memory Limit:65536KB 64bit IO Format:%I64d & %I64u

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Description

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.

Sample Input

Input

Output

如果直接用公式那样乘，会超出long long 类型范围，故需要边乘边除。

AC-code:

#include<cstdio>
#include<iostream>
using namespace std;
int main()
{
	long long n,ans,temp;
	int i,j; 
	cin>>n;
	ans=0;
	for(i=5;i<=7;i++)
	{
		temp=1;
		for(j=1;j<=i;j++)
			temp=temp*(n-j+1)/j;
		ans+=temp;
	}
	printf("%lld\n",ans);
}