#include<bits/stdc++.h>
#define range(i,a,b) for(int i = (a); i < (b); i++)
#define rep(i,b) range(i,0,b)
#define itrep(it, a) for(it = (a).begin(); it != (a).end(); it++)
#define all(a) (a).begin(), (a).end()
#define debug(x) cout << "debug " << x << endl;
#define INF (1 << 30)
using namespace std;

int main(){
    double q;
    while(cin >> q, q!=-1){
        double x = q / 2;
        while(abs(x * x * x - q) >= 0.00001 * q){
            x = x - (x * x * x - q) / (3 * x * x);
        }
        printf("%.6lf\n", x);
    }
}