#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#define popcount __builtin_popcount
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;

int main()
{
    double x;
    cin>>x;
    double ans=0;
    for(int i=1; i<=1000000; i++){
        ans+=1.0/((double)i+x)/((double)i+x);
    }
    ans+=1.0/(1000001.0+x);
    printf("%.10lf\n", ans);
    return 0;
}