#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
double ans(int q,double x){
x=x-(x*x*x-q)/(3*x*x);
if((x*x*x-double(q)<0.000001*double(q))&&(x*x*x-double(q)>-0.000001*double(q))){
return x;
}else{
return ans(q,x);
}
}
int main(){
int q;
double x;
while(scanf("%d",&q),q!=-1){
x=ans(q,double(q)/2);
printf("%lf\n",x);
}
}