#include<bits/stdc++.h>
using namespace std;
int main()
{
	int s;
	cin>>s;
	auto check=[&](long long lim)
	{
		long long ret=0;
		long long X=0,Y=1;
		while((X+1)*(X+1)+Y*Y<=lim)X++;
//		cerr<<"ini "<<X<<endl;
		ret+=X;
		long long t=X;
		while(Y<=t)
		{
			Y++;
			while(X>0 and X*X+Y*Y>lim)X--;
			ret+=X;
		}
//		cerr<<"check "<<lim<<" = "<<ret*4<<endl;
		return ret*4;
	};
	long long l=0,r=2e9;
	while(l<r)
	{
		long long mid=(l+r)/2;
		if(check(mid)>s)r=mid;
		else l=mid+1;
	}
	cout<<fixed<<setprecision(12)<<sqrt(1.*l)<<endl;
	return 0;
}