#include <bits/stdc++.h>
using namespace std;
#define ll long long
int tt, tc;

void solve() {
	ll s;
	cin >> s;

	auto check = [&](long double radius) {
		ll max_height = round(floor(radius));
		ll num_sq = 0;
		for (int i = 1; i <= max_height; i++) {
			// x^2 + y^2 = radius^2
			// x^2 = radius^2 - y^2
			long double h = i;
			long double x = sqrt(radius * radius - h * h);
			num_sq += (ll)round(floor(x));
		}
		num_sq <<= 2;
		return num_sq >= s + 1;
	};

	long double l = 0, r = 1e6;
	int ctr = 100;
	while (ctr--) {
		long double mid = (l + r) / 2.0;
		if (check(mid)) r = mid;
		else l = mid;
	}
	cout << fixed << setprecision(9) << r << "\n";
}

int main() {
	ios::sync_with_stdio(0); cin.tie(0);
	tt = 1, tc = 1; // cin >> tt;
	while (tt--) solve(), tc++;
}