#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < n; ++i)
#define ALL(c) (c).begin(), (c).end()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v, x) (std::find(v.begin(), v.end(), x) != v.end())
using namespace std;

typedef long long ll;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
const int INF = 1e9;
const long long INFL = 1LL<<60;

int main()
{
  ll n, k;
  cin >> n >> k;
  ll sum = 0;
  for (ll i = 0; i <= n; i++) {
    sum += i * k;
  }
  cout << sum / double((n+1) * k) << endl;
  return 0;
}