#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 1e9 + 10;
const ll INFL = 4e18;

int main() {
    ll N;
    cin >> N;

    double ans = 0;
    double d = 1e-5;
    for (double x = 0; abs(x - 1) > 1e-5; x += d) ans += sqrt(x * x * x + N * N * N) * d;

    printf("%.10f\n", ans);
}