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

double q;

int main() {
  while (1) {
    scanf("%lf", &q);
    if (q == -1.0) return 0;
    
    double ans = q/2;
    while (abs(ans*ans*ans - q) >= 1e-5*q) {
      ans = ans - (ans*ans*ans-q)/(3*ans*ans);
    }

    printf("%f\n", ans);
  }
}