化简

#include <stdio.h>

//求阶乘
long long Factor(int n,int r)
{
	int i = n-r+1;
	long long s = 1;
	while(i <= n)
	{
		s*=i;
		i++;
	}
	return s;
}

int main()
{
	int n,r;
	while(scanf("%d %d",&n,&r) != EOF)
	{
		if(n == 0 && r == 0) break;
		else if(n < r) printf("error!\n");
		else printf("%lld\n",Factor(n,r)/(Factor(r,r)));
	}
	return 0;
}