POJ 2249

#include<stdio.h>
longlong sum;
int main()
{
int k,n,m;
while(~scanf("%d%d",&n,&m)&&(n!=0||m!=0))
{
sum =1;
m = m<(n-m)?m:n-m;
for(k =1;k <= m;k++)
sum =(sum*(n-m+k))/k;
printf("%lld\n",sum);
}
return0;}