Contest1472/I.cpp

#include<bits/stdc++.h>
using namespace std;
using ll = long long;
ll Cnr(int n, int r) {
    ll s = 1;
    if (r * 2 > n) {
        r = n - r;
    }
    for (int i = 0; i < r; i++) {
        s *= (n - i);
    }
    for (int i = r; i >= 2; i--) {
        s /= i;
    }
    return s;
}
int main() {
    int n, r;
    while (cin >> n >> r) {
        cout << Cnr(n, r) << endl;
    }
    return 0;
}