#include<cstdio>
#include<algorithm>
#include<vector>
#include<string>
#include<iostream>
#include<queue>
#include<map>
#include<set>
#include<complex>
#include<stack>
#include<cmath>
 
using namespace std;
 
#define reps(i,f,n) for(int i=f;i<int(n);i++)
#define rep(i,n) reps(i,0,n)

int main(){
	
	int a;
	while(cin>>a){
		if(a==-1)break;
		
		double q = a;
		double x = q/2;
		rep(i,200){
			x = x-(x*x*x-q)/(3*x*x);
		}
		
		printf("%.9lf\n",x);
	}
	
}