#include <bits/stdc++.h>
using namespace std;
#define rep(i, s, e) for (ll i = s; i < e; ++i)
#define sort_(a) sort(a.begin(), a.end())
#define rsort(a) sort(a.rbegin(), a.rend())
#define sum(a) accumulate(a.begin(), a.end(), 0LL)
#define __lcm(a, b) std::__detail::__lcm(a, b)
typedef long long unsigned int ll;
const long mod = 1e9 + 7;

int main(void) {
#ifdef DEBUG
  freopen("input.txt", "r", stdin);
#endif

  ios_base::sync_with_stdio(false);
  cin.tie(0);

  ll N, K;
  cin >> N >> K;
  ll deno = (N + 1) * K;
  ll nume = 0;
  rep(i, 0, N + 1) {
    nume += i * K;
  }
  double ans = (double)nume / deno;
  printf("%.10f\n", ans);
  return 0;
}