/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.06.12 23:24:44
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int main() {
    double p; cin >> p;
    printf("%.10f\n",1/(1-p)-1);
    return 0;
}