#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    double p;
    cin >> p;

    printf("%.8f\n", 1 / (1 - p) - 1);

    return 0;
}