#include <bits/stdc++.h>
using namespace std;

#define FOR(i,l,r) for(int i = (int) (l);i < (int) (r);i++)
template<typename T> bool chmax(T& a,const T& b){ return a < b ? (a = b,true) : false; }
template<typename T> bool chmin(T& a,const T& b){ return b < a ? (a = b,true) : false; }
typedef long long ll;

ll N;

int main()
{
	while(scanf("%lld",&N),N != -1){
		double x = N / 2.0;
		do{
			x = x - (x * x * x - N) / (3 * x * x);
		}while(abs(x * x * x - N) >= 0.00001 * N);
		printf("%.10f\n",x);
	}

	return 0;
}