#include <bits/stdc++.h>
#define int long long
#define double long double
using namespace std;
const int MOD = 1000000007;
const int INF = 1e14;
using Graph = vector<vector<int>>;

signed main(){
  int N, K;
  cin >> N >> K;
  int A = 0;
  for( int i = 1; i <= N; i++ ) A += i*K;
  double ans = (double)A/((double)(N+1)*(double)K);
  cout << ans << endl;
}