#include<bits/stdc++.h>
#define loop(i,a,b) for(int i=a;i<b;i++)
#define rep(i,a) loop(i,0,a)
using namespace std;

int main(){
	double q=0,alt1=0,alt2=0;
	while(1){
		cin>>q;
		if(q==-1)break;
		alt1=q/2.0;
		alt2=alt1-(pow(alt1,3)-q)/(3*pow(alt1,2));
		while(abs(alt2-alt1)>=0.000001*q){
			alt1=alt2;
			alt2=alt1-(pow(alt1,3)-q)/(3*pow(alt1,2));
		}
		printf("%.9f\n",alt2);
	}
	return 0;
}