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

int main() {

  long long int in;

  while( true ) {

    cin >> in;

    if ( in == -1 ) break;

    double x = 0.50 * in;

    while( abs( x * x * x - in ) >= 0.00001 * in ) {

      x = x - ( x * x * x - in ) / ( x * x * 3 );

    }

    cout << fixed << setprecision(8) << x << endl;

  }

  return 0;

}