#include <stdio.h>
#include <math.h>

#define ABS(x) ((x) < 0 ? -1 * x : x)

double q;

double tr(double x){
  if(ABS(pow(x, 3) - q) < 0.00001 * q) return x;
  return tr(x - ((pow(x, 3) - q) / (3 * pow(x, 2))));
}

int main(){
  while(scanf("%lf", &q) && q != -1)
    printf("%.6f\n", tr(q / 2));
  return 0;
}