#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <complex>
using namespace std;

#define REP(i,n) for(int i=0;i<(int)n;++i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()

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