#include<iostream>
#include<string.h>
#include<cstdio>
#include<algorithm>
#include<stack>
#include<queue>
#include<vector>
#include<cmath>
#include<utility>
#define ll long long int
#define ld long double
#define INF 1000000000
#define EPS 0.0000000001
#define rep(i,n) for(i=0;i<n;i++)
using namespace std;
typedef pair<int, int> P;

string str;

int main()
{
  int x;

  while(1){
    cin>>x;
    if(x<0)break;
    double a,b;
    b=x/2;

    while(2){
      a=b-(b*b*b-x)/(3*b*b);
      if(abs(a*a*a-x)<0.00001*x)break;
      b=a;
    }
    cout<<a<<endl;
  }
}