#include <bits/stdc++.h>
using namespace std;
int main(){
    double temp=0;
    double epsilon=pow(10,-10);
    double n=1;
    double x;
    cin>>x;
    while(1/(n+x)-1/(n+x+1)>epsilon){
        temp+=1/(n+x)/(n+x);
        ++n;
    }
    printf("%.10f",temp+1/(n+x));
}