#include<cstdio>
#include<cmath>
int main(void){
  double q,x;
  for( ; ; ){
    scanf("%lf",&q);
    if(q == -1) break;
    x = q / 2;
    while(fabs(pow(x,3) - q) >= 0.00001 * q) x = x - ((pow(x,3) - q) / (3 * pow(x,2)));
    printf("%.6f\n",x);
  }
}
