#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef long double ld;
typedef pair<int,int> P;
constexpr int INF = 2e9;
constexpr int AMAX = 10001;
int main() {
  ld p;
  cin >> p;
  ld res = 0;
  printf("%.12LF\n",p * (1.0 / (1 - p)));
  return 0;
}