#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;

#define EPS 1e-5

int main() {
  
  double q;
  while( cin >> q, q >= 0 ) {
    double x = q/2;
    while( fabs( x*x*x ) >= EPS * q ) {
      x = x - ( x*x*x - q ) / ( 3*x*x );
    }
    printf("%f\n", x);
  }
  
  return 0;
}