#include <bits/stdc++.h>
#define range(i,a,b) for(int (i)=(a);(i)<(b);(i)++)
#define rep(i,n) range(i,0,n)
using namespace std;

int main(void){
	int q;
	while(cin >> q){
		if(q==-1) break;
		double x=1.0*q/2.0;
		while(abs(x*x*x-q)>0.000001*q){
			x=x-(x*x*x-q)/(3.0*x*x);
		}
		cout.precision(6);
		cout << fixed << x << endl;
	}
	return 0;
}