#include<map>
#include<set>
#include<list>
#include<cmath>
#include<queue>
#include<stack>
#include<cstdio>
#include<string>
#include<vector>
#include<complex>
#include<cstdlib>
#include<cstring>
#include<numeric>
#include<sstream>
#include<iostream>
#include<algorithm>
#include<functional>

#define mp       make_pair
#define pb       push_back
#define all(x)   (x).begin(),(x).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define REP(i,b,n) for(int i=b;i<n;i++)

using namespace std;

typedef    long long          ll;
typedef    unsigned long long ull;
typedef    vector<bool>       vb;
typedef    vector<int>        vi;
typedef    vector<vb>         vvb;
typedef    vector<vi>         vvi;
typedef    pair<int,int>      pii;

const int INF=1<<29;

const int dx[]={1,0,-1,0},dy[]={0,-1,0,1};

int main(){
	ll q;
	while(cin>>q){
		if(q==-1)break;
		const double EPS=(1e-5);
		double x=q/2;
		while(true){
			x =x-(pow(x,3)-q)/(3*pow(x,3));
			if(abs(pow(x,3)-q)<EPS*q)break;
		}
		printf("%,7f\n",x);
	}

	return 0;
}