#include <bits/stdc++.h>
using namespace std;

#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define REP(i, n) for (int i = 0; i < (n); i++)

int main()
{
  double q, x, cx;

  while (scanf("%lf", &q), q != -1){
    x = q * 0.5;
    while (abs(x * x * x - q) >= (0.00001 * q)){
      x = x - (x * x * x - q) / (3 * x * x);
    }
    printf("%.6f\n", x);
  }
}