#include<bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint=modint998244353;
using namespace std;
using ll=long long;
using ul=unsigned long long;
int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1};
int dy[8] = {0, 0, -1, 1, -1, 1, -1, 1};
using Graph=vector<vector<int>>;
int main(){
    double a;
    cin>>a;
    cout<<fixed<<setprecision(10)<<1.0/(1.0-a)-1.0<<endl;
}