#include<bits/stdc++.h>
using namespace std;
typedef double db;
const db eps=1e-9;
typedef long long ll;

int s=0;

bool check(db mid)
{
	ll cnt=0;
	for(int i=1;i<=mid;i++)
	{
		db d=mid*mid-1ll*i*i;
		// cerr<<"i = "<<i<<", d = "<<d<<": \n";
		int l=0,r=mid+1;
		while(l+1<r)
		{
			// cerr<<l<<" "<<r<<"\n";
			int m=l+r>>1;
			if(1ll*m*m<=d) l=m;
			else r=m;
		}
		cnt+=l;
	}
	// cerr<<"mid = "<<mid<<", cnt = "<<cnt<<"\n";
	return 4*cnt>s;
}

int main()
{
	scanf("%d",&s);
	db l=0,r=sqrt(s);
	while(l+eps<=r)
	{
		db mid=l+(r-l)*0.5;
		// cerr<<l<<" "<<r<<" "<<mid<<": \n";
		if(check(mid)) r=mid;
		else l=mid;
		// cerr<<"\n";
	}
	printf("%.20lf\n",r);
	return 0;
}