#include <bits/stdc++.h>
using namespace std;
const double PI = acos(-1);
const int N = 1e5 + 5;
const int MOD = 1e9 + 7;
long long sum(long long a, long long b) {
  a += b;
  if (a < 0) return a + MOD;
  if (a >= MOD)
    return a - MOD;
  else
    return a;
}
long long mult(long long a, long long b) {
  long long c = 1LL * (a % MOD) * (b % MOD);
  return c % MOD;
}
int poww(long long a, long long b) {
  long long res = 1;
  a %= MOD;
  while (b > 0) {
    if (b % 2) res = (res * a) % MOD;
    a = (a * a) % MOD;
    b >>= 1;
  }
  return res % MOD;
}
int arr[16] = {2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53};
long long brr[16];
const long long INF = 1e18;
vector<long long> ans;
long long now = 1;
int n;
int CAP;
const int K = 8;
void rec(int cur) {
  if (cur == CAP) {
    ans.push_back(now);
  } else {
    if (now < brr[cur]) {
      long long keep = now;
      now *= arr[cur];
      rec(cur);
      now = keep;
    }
    rec(cur + 1);
  }
}
long long mx(long long mid, long long cur) { return mid / cur; }
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  int k;
  cin >> k;
  for (int i = 0; i < n; i++) {
    brr[i] = (INF + arr[i]) / arr[i];
  }
  if (n <= K) {
    CAP = n;
    rec(0);
    sort(ans.begin(), ans.end());
    cout << ans[k - 1] << endl;
    return 0;
  } else {
    CAP = K;
    rec(0);
    vector<long long> ans2 = ans;
    ans.clear();
    CAP = n;
    rec(K);
    if (ans.size() > ans2.size()) {
      ans2.swap(ans);
    }
    sort(ans.begin(), ans.end());
    sort(ans2.begin(), ans2.end());
    long long l = 0, r = 1e18 + 1;
    while (l + 1 < r) {
      long long mid = (l + r) / 2;
      long long cur = 0;
      for (int i = 0; i < ans.size(); i++) {
        long long m = mx(mid, ans[i]);
        auto it = upper_bound(ans2.begin(), ans2.end(), m);
        cur += it - ans2.begin();
      }
      if (cur < k)
        l = mid;
      else
        r = mid;
    }
    cout << r << endl;
  }
  return 0;
}
