#include <bits/stdc++.h>
#define rep(i, a, n) for (int i = a; i < n; i++)
#define repr(i, a, n) for (int i = n - 1; i >= a; i--)
using namespace std;
using ll = long long;
using P = pair<int, int>;
template <typename T> void chmin(T &a, T b) { a = min(a, b); }
template <typename T> void chmax(T &a, T b) { a = max(a, b); }

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  int n, k;
  cin >> n >> k;

  double b = (n + 1) * k;
  double ans = 0;
  rep(i, 0, n + 1) { ans += i * k; }
  double xxx = ans * (1 / b);
  cout << fixed << setprecision(10) << xxx << endl;
}