#include<iostream>
using namespace std;
int comb(int n, int r)
{
	if (r == 0)
		return 1;
	else if (r == 1)
		return n;
	else
		return (comb(n, r-1) * (n - r + 1)) / r;
}
int main()
{
	int n, r;
	while (1) {
		cin >> n >> r;
		if (n == 0 && r == 0)
			break;
		if (n < 0 || r < 0 || n < r) {
			cout << "error!" << endl;
			continue;
		}
		cout << comb(n, r) << endl;
	}
	return 0;
}