#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;


int main(){
  ll N, K;
  cin >> N >> K;

  double ret = 0;
  rep(i,N+1){
    ret += i * K;
  }
  ret /= (N+1) * K;

  printf("%.12lf\n", ret);
  
  return 0;
}