#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;
double z2=1.6449340668482264;
int main()
{
    double x;
    cin>>x;
    int k=(int)x;
    double ans=0;
    for(int i=1; i<=100000; i++){
        ans+=1.0/((double)i+x)/((double)i+x);
    }
    double r=z2;
    for(int i=1; i<=k+100000; i++){
        r-=1.0/((double)i)/((double)i);
    }
    double t=0;
    for(int i=100001; i<=10000000; i++){
        t+=1.0/((double)(i+k))/((double)(i+k))/((double)(i+k));
    }
    r-=2.0*t*(x-(double)k);
    ans+=r;
    printf("%.10lf\n", ans);
    return 0;
}