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

int main()
{
    int q;
    while(cin >> q)
    {
        if(q==-1)break;
        double qz = (double)q;
        double x=1;
        double e;
        while(1)
        {
            e = x*x*x-qz;
            x= x-e/(3*x*x);
            if(fabs(e)*100000 < qz) break;
        }
        printf("%6f\n",x);
    }
    

    return 0;
}