Codeforces 630F - Selection of Personnel

http://www.codeforces.com/problemset/problem/630/F

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

//排列组合 计算Cn5+Cn6+Cn7的值

#include <cstdio>
//33319741730082870
#define LL __int64
LL zuHe(LL n,int m)
{
if(n<m) return 0;
if(n==m) return 1;
LL ans=1;
int j=2;
for(int i=n-m+1;i<=n;++i)
{
ans*=i;
while(j<=m&&ans%j==0)
{
ans/=j;
++j;
}
}
while(j<=m)
{
ans/=j;
++j;
}
return ans;
}
int main()
{
LL n;
while(~scanf("%I64d",&n))
{
LL ans=0;
for(int i=5;i<=7;++i)
{
ans+=zuHe(n,i);
}
printf("%I64d\n",ans);

}
return 0;
}