#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main(){
double x,y,q;
while(cin>>q){
if(q==-1)break;
x=q*0.5;
for(;;){
y=x*x*x-q;
if(fabs(y)<0.00001*q)break;
x-=y/(3*x*x);
}
printf("%.6f\n",x);
}
return 0;
}