Input

The input will contain one or more test cases.

Each test case consists of one line containing two integers n (n >= 1) and k (0 <= k <= n).

Input is terminated by two zeroes for n and k.

Output

For each test case, print one line containing the required number. This number will always fit into an integer, i.e. it will be less than 2^31.

Sample Input

4 2
10 5
49 6
0 0

Sample Output

6
252
13983816

求C(n,k)，但是要注意是C(n,k)快還是C(n,n-k)快

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>

using namespace std;

int min(int a,int b){
    return a>b?b:a;
}

long long cal(int n,int k){
    long long ret = 1;
    k = min(k,n-k);
    for( int i = 0 ; i < k ; ++i )
        ret = (ret * (n-i) / (i+1) );
//    for( int i = 2 ; i <= k ; ++i )
//        ret /= i;
    return ret;
}

int main(){
    int n,k;
    while( ~scanf("%d %d",&n,&k) ){
        if( !n&&!k ) break;
        printf("%lld\n",cal(n,k));
    }
    return 0;
}