组合数

#include <iostream>using namespace std;long fac (int n){int sum=1,i=1;for (i=1;i<=n;i++)sum=sum*i;return sum;}long fac (int n,int m){int sum=1,i=1;for (i=1 ;i<=(m-n);i++)sum=sum*i;return sum;}int main (){int m,n,a;cin>>n>>m;a=fac(n)*fac(n,m);cout<<fac(m)/a;return 0;}