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

int main() {
	int64_t n; cin >> n;
	int64_t k; cin >> k;
	double ans = (double)(k * (n * (n + 1) / 2)) / (double)((n + 1) * k);
	printf("%.10f\n", ans);

	return 0;
}