#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
	cin.tie(nullptr)->sync_with_stdio(false);
	int s;
	cin >> s;
	double low = 0; double high = 1e5;
	for(int iters = 0; iters < 120; iters++){
		double r = (low+high)/2;
		int ans = 0;
		for(int i = 1; i<=r; i++){
			//x^2 + y^2 = r^2
			// x = sqrt(r^2 - y^2);
			int v = sqrt(r*r - i*i);
			ans+=v*4;
		}
		if(ans>s){
			high = r;
		}
		else{
			low = r;
		}
	}
	cout << fixed << setprecision(12);
	cout << high << '\n';
	return 0;
}