HW1_cnk

#include <cstdio>

int main()
{
    int n = 0, k = 0, ans = 1;
    scanf("%d", &n);
    scanf("%d", &k);
    if (k > n || k < 0 || n < 0)
    {
        printf("%d\n", ans - 1);
    }
    else
    {
        for (int i = k + 1; i <= n; ++i)
        {
            ans = ans * i / (i - k);
        }
        printf("%d\n", ans);
    }
    return 0;
}