#include<bits/stdc++.h>
using namespace std;
#define all(vec) vec.begin(),vec.end()
typedef long long int ll;
const ll MOD=1000000007;
const ll INF=1000000010;
const ll LINF=4000000000000000010LL;
const int MAX=310;
const double EPS=1e-8;
int dx[4]={0,0,1,-1};
int dy[4]={-1,1,0,0};
int main(){
	double q;
	while(cin>>q,q!=-1){
		int id=0;
		double dp[100010];
		dp[0]=q/2;
		while(abs(pow(dp[id],3)-q)>EPS){
			dp[id+1]=dp[id]-(pow(dp[id],3)-q)/(3*pow(dp[id],2));
			id++;
		}
		printf("%.8lf\n",dp[id]);
	}
		
}

