#include <bits/stdc++.h>
using namespace std;
using i64 = int64_t;
using vi = vector<i64>;
using vvi = vector<vi>;
#pragma GCC optimize("O3")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    cout.setf(ios::fixed);
    cout.precision(20);
    double x;
    cin >> x;
    long double y = x;

    long double sum = 0;
    for (int i = 1; i <= 1100000000; i++) {
        long double t = y + i;
        t = t * t;
        sum += 1.0 / t;
    }

    double k = sum;
    cout << k << endl;
}