#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<int, int> PII;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define MP make_pair
#define PB push_back
#define MOD 1000000007
#define INF (1LL<<30)
#define LLINF (1LL<<60)
#define PI 3.14159265359
#define EPS 1e-12
#define int ll

signed main(void)
{
  while(true) {
    long double q;
    cin >> q;
    if(q == -1) break;
    long double a = q/2;
    REP(i, 1000000) {
      a = a-(a*a*a-q)/(3*a*a);
    }
    cout << fixed << setprecision(15) << a << endl;
  }
  return 0;
}