#include <iostream>

using namespace std;

int main() {

	long long int N, K;
	cin >> N >> K;

	long long int denom = (N + 1) * K;
	long long int numer = 0;
	for (long long int i = 0; i <= N; i++) {
		numer += i * K;
	}

	double ans = static_cast<double>(numer) / denom;
	cout << ans << endl;

	return 0;

}