ZOJ 1938 Binomial Showdown

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