include <bits/stdc++.h>

using namespace std; int main(){

int a;
cin>>a;
double x0=a;
double x1=x0*2/3+a/(3*x0*x0);
do{
	x0=x1;
	x1=x0*2/3+a/(3*x0*x0);
}while(fabs(x1-x0)>0.00001);
cout<<fixed<<setprecision(3)<<x1<<endl;
return 0;

}