poj 2249（水题，组合数，大数）

#include<iostream>
#include<cstdio>
using namespace std;
int main(){
    long long n,k,i,j,sum;
    while(scanf("%lld%lld",&n,&k)==2&&n){
        if(n-k<k){
            k = n-k;
        }
        sum = 1;
        for(i=1,j=n-k+1;i<=k;i++,j++){
            sum = sum*j/i;
        }
        printf("%lld\n",sum);
    }
    return 0;
}