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

bool check(ll x, ll s, ll dx, ll dy) {
	// cout << dx << ' ' << dy << endl;
	ll cnt = 0;
	for (ll i = 1; (2 * i - dx) * (2 * i - dx) <= x; ++i) {
		ll l = 0, r = sqrt(x);
		ll res = x - (2 * i - dx) * (2 * i - dx);
		while (l <= r) {
			ll mid = (l + r) >> 1;
			if ((2 * mid + dy) * (2 * mid + dy) <= res)
				l = mid + 1;
			else 
				r = mid - 1;
		}
		// cout << l << ',' << i << ',' << x << endl;
		// cout << res << endl;
		cnt += ((l - 1) * 2 + dy) * (1 + !(dx && i == 1));//, cout << cnt << ',';
	}
	// cout << x << ':' << cnt << ',' << s << endl;
	return cnt < s;
}
int main() {
	ll s;
	cin >> s;
	ll ans = 0x3f3f3f3f;
	{
		ll ss = (s + 3) / 4 * 4;
		// cout << s << endl;
		ll l = 0, r = 5 * ss;
		while (l <= r) {
			ll mid = (l + r) / 2;
			if(check(mid, ss, 0, 0))
				l = mid + 1;
			else 
				r = mid - 1;
		}
		ans = min(ans, l);
	}
	{
		ll l = 0, r = 5 * s;
		while (l <= r) {
			ll mid = (l + r) / 2;
			if(check(mid, s, 1, 1))
				l = mid + 1;
			else 
				r = mid - 1;
		}
		// cout << l << endl;
		ans = min(ans, l);
	}
	{
		ll l = 0, r = 5 * s;
		while (l <= r) {
			ll mid = (l + r) / 2;
			if(check(mid, s, 1, 0))
				l = mid + 1;
			else 
				r = mid - 1;
		}
		// cout << l << endl;
		ans = min(ans, l);
	}
	// cout << ans << endl;
	cout << fixed << setprecision(10) << sqrt(ans / 4.0) << '\n';
}