A - Rooks (24-11)

#include <bits/stdc++.h>
#define ll long long
using namespace std;

ll calcNcR(int n, int r) {
    ll p = 1, k = 1;

    if(n - r < r) r = n - r;
    if(r != 0)

        while(r) {
            p *= n; k *= r;

            long long m = __gcd(p, k);
            p /= m; k /= m;
            n--; r--;
        }
    else p = 1;

    return p;
}

void solve(int test) {
    int n, k; cin >> n >> k;

    ll ans = 0;
    if(n < k) cout << "Case " << test << ": " << ans << "\n";
    else {
        ans = calcNcR(n, k) * calcNcR(n, k);

        //k giai thua
        for(ll i = 1; i <= k; ++i)
            ans *= i;

        cout << "Case " << test << ": " << ans << "\n";
    }
    return;
}

int main() {
    //freopen("A-Rooks.inp", "r", stdin);
    //freopen("A-Rooks.out", "w", stdout);
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);

    int t; cin >> t;
    for(int i = 1; i <= t; i++) {
        solve(i);
    }

    return 0;
}