#include <bits/stdc++.h>
using namespace std;

void fast_io() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
}

int main() {
	fast_io();
	int n;
	cin >> n;
	auto f = [&](double x) { return sqrt(x * x * x + n * n); };
	double ans = 0;
	int int_num = 1e4;
	for (int i = 0; i < int_num; i++) {
		double l = (double)i / int_num;
		double r = (double)(i + 1) / int_num;
		ans += (r - l) / 6 * (f(l) + 4 * f((l + r) / 2) + f(r));
	}
	cout << setprecision(16) << fixed << ans << endl;
}