#include <bits/stdc++.h>
using namespace std;
inline long long readi() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
void search(const vector<int> &p, vector<long long> &a, int x, long long num,
            long long budget) {
  while (x != -1 && budget < p[x]) x--;
  if (x == -1) {
    a.push_back(num);
    return;
  }
  long long cur = 1;
  while (cur <= budget) {
    search(p, a, x - 1, num * cur, budget / cur);
    if (budget / cur < p[x]) break;
    cur *= p[x];
  }
}
int n;
vector<int> p, q;
vector<long long> a, b;
long long k;
long long get(long long budget) {
  long long res = 0;
  for (long long num : a) {
    if (num > budget) break;
    res += upper_bound(b.begin(), b.end(), budget / num) - b.begin();
  }
  return res;
}
int main() {
  n = readi();
  for (int i = 0; i < n; i++) {
    int num = readi();
    if (i & 1)
      q.push_back(num);
    else
      p.push_back(num);
  }
  k = readi();
  long long mx = 1e18;
  search(p, a, p.size() - 1, 1, mx);
  search(q, b, q.size() - 1, 1, mx);
  sort(a.begin(), a.end());
  sort(b.begin(), b.end());
  long long lo = 1, hi = mx;
  while (lo < hi) {
    long long mid = lo + hi >> 1;
    if (get(mid) >= k)
      hi = mid;
    else
      lo = mid + 1;
  }
  cout << lo << endl;
  return 0;
}
