#include <cassert>
#include <iostream>
#include <vector>
#include <algorithm>
#include <utility>
#include <iomanip>

#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define RFOR(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep1(i, n) for (int i = 1; i <= (n); i++)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)

#define pb push_back
#define mp make_pair
#define fst first
#define snd second
#define show(x) cout << #x << " = " << x << endl
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define pii pair<int, int>
#define vi vector<int>

using namespace std;
template <class S, class T>
ostream& operator<<(ostream& o, const pair<S, T>& p)
{
    return o << "(" << p.first << "," << p.second << ")";
}
template <class T>
ostream& operator<<(ostream& o, const vector<T>& vc)
{
    o << "sz = " << vc.size() << endl
      << "[";
    for (const T& v : vc)
        o << v << ",";
    o << "]";
    return o;
}
typedef long long ll;

constexpr long double EPS = 0.000000001;
long double err(long n, long double x)
{
    return (1.0 / (n + x)) * (1.0 / (n + x + 1));
}

int main()
{
    long double x;
    cin >> x;
    constexpr long N = 100000;
    long double sum = 1.0 / (x + N);
    for (long i = N; i >= 1; i--) {
        sum += (1.0 / (i + x)) * (1.0 / (i + x));
    }
    cout << std::setprecision(17) << sum << endl;


    return 0;
}