#include<iostream>
#include<cmath>
using namespace std;
int main(){
	int n;
	while(cin >>n){
		if(n == -1){break;}
		double x = n/2;
		for(;;){
			if(fabs(x*x*x-n)<0.00001*n){break;}
			x = x-(x*x*x-n)/(3*x*x);
		}
		cout <<x<<endl;
	}
	return 0;
}