#include<bits/stdc++.h>
using namespace std;
long const mod = 1e9+7;
int main(){
    int k;
    cin >> k;
    double ans = 0;
    for(double i = 1.0;i< 1000000;i+=1.0){
        ans += 1.0 / (i * (i + (double)k));
    }
    printf("%.10lf\n",ans);
}