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

int main() {
	float n, k;
	cin >> n >> k;

	float s = 0,
		a = (n + 1) * k;
	for (float i = 0; i < n+1; i++) {
		s += i * k;
	}

	cout << fixed << setprecision(5) << s / a << endl;
}