#include<iostream>
#include<cmath>
#include<cstdio>

using namespace std;

double ThirdRoot(double q){
	double ret = q/2;
	while( true ){
		if( fabs(pow(ret,3.0) - q) < 0.00001*q ) break;
		ret = ret - ((pow(ret,3.0) - q) / (3 * pow(ret, 2.0)));
	}
	return ret;
}

int main(void){
	while( true ){
		int q;
		
		cin >> q;
		if( q == -1 ) break;

		printf("%lf\n", ThirdRoot((double)q));
	}
	return 0;
}