#include <cstdio>
#include <cmath> 
using namespace std; 
int main() {
double q,x; 
while(scanf("%lf",&q), q!=-1) {
x=q/2.0; 
while(abs(x*x*x-q) >= 0.00001*q) { 
x = x-(x*x*x-q)/(3*x*x); 
} 
printf("%.6lf\n",x); 
} 
}

