#include <stdio.h>
#include <cmath>
#include <algorithm>

using namespace std;


int main(){

    double q,tmp,next,limit;

    while(true){
    	scanf("%lf",&q);
    	if(q == -1)break;

    	limit = 0.00001*q;
    	tmp = q/2;
    	next = q/2;

    	while(fabs(next*next*next-q) >= limit){
    		tmp = next;
    		next = tmp - (tmp*tmp*tmp-q)/(3*tmp*tmp);
    	}

    	printf("%.6lf\n",next);

    }

    return 0;
}