#include <iostream>
#include <vector>
#include <iomanip>
#include <cmath>
using namespace std;
int num(int a)//a代表r*r 
{
	int res=0;
	for(int i=int(sqrt(a));i>0;i--)
	res+=int(sqrt(a-i*i));
	res*=4;
	return res;
}
int main()
{
	int n;
	cin>>n;
	n++;
	int r=sqrt(n);
	int l=r/3;
	int mid;
	while(l<r)
	{
		mid=(l+r)/2;
		int t=num(mid*mid); 
		if(t>=n)r=mid;
		if(t<=n)l=mid;
		//cout<<"l"<<l<<" "<<"r"<<r<<endl;
		if(l+1==r)break;
	}
	mid=(l+r)/2;
	int b=mid*mid;
	int e=(mid+1)*(mid+1);
	for(int i=b;i<=e;i++)
	{
		if(num(i)>=n)
		{
			cout<<fixed<<setprecision(10)<<sqrt(i);
			break;
		}
	}
	return 0;
}