#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() {
  double p;
  cin >> p;
  cout << fixed << setprecision(15) << 1/(1-p)-1 << endl;


}