#include <bits/stdc++.h>
#ifdef _DEBUG
#include "debug.hpp"
#else
#define debug(...)
#endif
#define fastIO (cin.tie(0), cout.tie(0), ios::sync_with_stdio(false))
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define precise(i) fixed << setprecision(i)
using ll = int64_t;
using ul = uint64_t;
using namespace std;
using std::cout;

void solve() {
  ul n, k;
  cin >> n >> k;

  ul den = (n + 1) * k;
  ul poss = 0;
  for (int i = 0; i <= n; i++) {
    poss += i * k;
  }

  cout << precise(10) << (poss / (double)den) << endl;
}

void wrapper() {
  rep(i, 2) {
    cout << "[TEST " << (i + 1) << "]\n";
    solve();
    cout << "\n";
  }
}

int main() {
  fastIO;
#ifdef _DEBUG
  wrapper();
#else
  solve();
#endif
}