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

int main()
{
	int N, K;
	cin >> N >> K;

	double ans = 0;
	for( int n = 0; n <= N; n++ ) {
		ans += n * K;
	}
	ans /= (N + 1) * K;

	cout << fixed << setprecision(12) << ans << endl;
}