`@` C++:

#include <bits/stdc++.h>
#define int long long
#define ft(a, b, c) for (int i = a; i < b; i += c)

using namespace std;

int Rn(int n, int k)
{
    if (k > n - k) k = n - k;
    int ans = 1;
    ft(0, k, 1)
    {
        ans *= (n - i);
        ans /= (i + 1);
    }
    return ans;
}

signed main()
{
    int n, k; cin >> n >> k;
    cout << Rn(n, k);
}

$\color{Turquoise}{\triangleright \triangleright\ \color{ Turquoise}{\texttt{ItzPhuc} \triangleleft \triangleleft}}$