#include <bits/stdc++.h>

using namespace std;
using LL = long long;
using ULL = unsigned long long;
using VI = vector<int>;
using VL = vector<LL>;
using PII = pair<int, int>;
using PLL = pair<LL, LL>;
using ld = long double;

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define MP make_pair
#define PB push_back
#define EB emplace_back
#define F first
#define S second
#define FOR(i, a, b) for (int i = (a); i<(b); ++i)
#define RFOR(i, b, a) for (int i = (b)-1; i>=(a); --i)
#define FILL(a, b) memset(a, b, sizeof(a))

LL f(int r2)
{
	LL ans = 0;
	LL x = 1;
	while (x * x < r2)
	{
		LL y = sqrt(r2 - x * x) - 47;
		while (y < 0 || (y + 1) * (y + 1) + x * x <= r2) y++;
		ans += 4 * y;
		x++;
	}
	return ans;
}

void solve()
{
	int s;
	cin >> s;
	int l = 0, r = 1e9;
	while (l + 1 < r)
	{
		int m = (l + r) / 2;
		if (s > f(m))
			l = m;
		else
			r = m;
	}
	cout << fixed << setprecision(10) << sqrt(r) << '\n';
	
}

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int t = 1;
	//cin >> t;
	while (t--)
	{
		solve();
	}
}