#include <bits/stdc++.h>
#pragma GCC optimize(2)
using namespace std;
const long long INF = 1e18;
const int N = 2e5 + 7;
const int M = 5e6 + 7;
long long k;
vector<long long> s[2];
int p[20], a[20];
void dfs(int l, int r, long long x, int id) {
  s[id].push_back(x);
  for (int i = l; i <= r; i++)
    if (INF / x >= p[i]) dfs(i, r, x * p[i], id);
}
bool judge(long long x) {
  long long cnt = 0;
  for (int i = 0; i < s[0].size(); i++) {
    long long y = x / s[0][i];
    cnt += (upper_bound(s[1].begin(), s[1].end(), y) - s[1].begin());
  }
  return cnt < k;
}
signed main() {
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a[i];
  int cnt = 0;
  for (int i = 1; i <= n; i += 2) p[++cnt] = a[i];
  for (int i = 2; i <= n; i += 2) p[++cnt] = a[i];
  cin >> k;
  int hf = cnt / 2, _hf = n - hf;
  dfs(1, hf, 1, 0);
  sort(s[0].begin(), s[0].end());
  dfs(hf + 1, n, 1, 1);
  sort(s[1].begin(), s[1].end());
  long long l = 1, r = 1e18, mid;
  while (l < r) {
    mid = l + r >> 1ll;
    if (judge(mid))
      l = mid + 1;
    else
      r = mid;
  }
  cout << l << "\n";
}
