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

int main() {

    int N, K;
    cin >> N >> K;
    double n = (N+1) * K;
    cout << fixed << setprecision(20);
    double sum = (N + 1) * N * K / 2;
    cout << sum / n << endl;
    return 0;

}