#include <cstdio>
#include <cmath>
using namespace std;

int main(){
	double q, x;

	for(double q, x ; scanf("%lf", &q ) , q != -1 ; printf("%f\n" , x ) )
		for( x=q/2.0 ; fabs( x*x*x - q ) > 1e-5*q ; x = x - ( x*x*x-q ) / (3*x*x)  );
}