#include <iostream>
#include <cmath>
#include <cstdio>

using namespace std;
#define loop(i,a,b) for(int i=a; i<b; i++)
#define rep(i,b) loop(i,0,b)

int main(){
    int nq;
    while(1){
        cin>>nq;
        if(nq==-1) break;
        double q=nq,x=q/2;
        while(!(abs(x*x*x-q)<0.00001*q)){
            x=x-(x*x*x-q)/(3*x*x);
        }
        printf("%.10f\n",x);
    }
}