#include<bits/stdc++.h>
#define db double
#define ll long long
#define eps 5e-9
using namespace std;
template<typename T>
inline void read( T &n )
{
	n=0;bool w=false;char ch=getchar();
	while( ch>'9' || ch<'0' ) w=!(ch^'-'),ch=getchar();
	while( ch<='9' && ch>='0' ) n=(n<<3)+(n<<1)+(ch^48),ch=getchar();
	n=w?-n:n;
}
namespace kk
{///////////

ll count( db r )
{
	ll ret=0;
	for(int i=floor(r);i>=1;i--)
	{
		int l=floor(sqrt(r*r-1ll*i*i));
		while( 1ll*l*l+1ll*i*i>r*r ) l--;
		while( 1ll*(l+1)*(l+1)+1ll*i*i<r*r ) l++;
		ret+=l;
	}
	return ret<<2;
}

int s;
void solve()
{
	read(s);
	db l=1,r=1e5,ans;
	while( r-l>=eps )
	{
		db mid=(l+r)/2;
		if( count(mid)>=s ) 
			ans=mid,r=mid;
		else l=mid;
	}
	printf("%.8lf",ans);
}

}//////////
int main()
{
	kk::solve();
	return 0;
}