#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const long long INF = 1001001001;
const long long MOD = 1000000007;
const double EPS = 1e-10;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    int k;
    cin>>k;
    long double ans=0;
    for(ll i=1;;i++){
        ll t=i*(i+k);
        if(t>1e15)break;
        ans+=1.0/t;
    }
    cout<<fixed<<setprecision(12)<<ans<<endl;
}