#include <bits/stdc++.h>
using namespace std;
using ull = unsigned long long;

double calcExpectedValueDice(ull n, ull k) {
  ull sum = 0;
  for (ull i = 0; i <= n; ++i) sum += i;
  return (1.0 * sum / (n + 1));
}

void solve() {
  ull N, K;
  cin >> N >> K;
  cout << calcExpectedValueDice(N, K) << endl;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);
  solve();
  getchar();
}