#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

int main() {
  int n, k;
  cin >> n >> k;
  double ans = 0;
  rep(i,n+1) ans += i;
  cout << fixed << setprecision(10) << ans/(n+1) << endl;



}