#include <iostream>
#include <sstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <climits>
#include <cfloat>
using namespace std;

int main()
{
    for(;;){
        int q;
        cin >> q;
        if(q == -1)
            return 0;

        double x = q / 2.0;
        while(abs(pow(x, 3) - q) >= 0.00001*q)
            x -= (pow(x, 3) - q) / (3 * pow(x, 2));

        printf("%.6f\n", x);
    }
}