#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e18;
long long n, q;
vector<long long> fact[2];
vector<long long> rang[2];
void calcula(long long x, long long k, long long ac, long long t) {
  if (x == k) {
    rang[t].push_back(ac);
    return;
  }
  long long ans = 0;
  for (long long i = 0; i <= 62; i++) {
    if (ac <= INF) {
      calcula(x + 1, k, ac, t);
    } else {
      break;
    }
    if (ac > INF / fact[t][x]) {
      break;
    }
    ac *= fact[t][x];
  }
  return;
}
long long f(long long x) {
  long long ans = 0;
  for (long long i = 0; i < rang[0].size(); i++) {
    long long pos =
        upper_bound(rang[1].begin(), rang[1].end(), x / rang[0][i]) -
        rang[1].begin();
    ans += pos;
  }
  return ans;
}
long long bb(long long l, long long r, long long val) {
  while (l != r) {
    long long med = (l + r) / 2;
    if (f(med) < val) {
      l = med + 1;
    } else {
      r = med;
    }
  }
  if (f(l) < val) {
    l++;
  }
  return l;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.precision(10);
  cout << fixed;
  cin >> n;
  long long x;
  for (long long i = 0; i < n; i++) {
    cin >> x;
    fact[i % 2].push_back(x);
  }
  reverse(fact[0].begin(), fact[0].end());
  reverse(fact[1].begin(), fact[1].end());
  cin >> q;
  calcula(0, fact[0].size(), 1, 0);
  calcula(0, fact[1].size(), 1, 1);
  sort(rang[0].begin(), rang[0].end());
  sort(rang[1].begin(), rang[1].end());
  cout << bb(1, INF, q) << endl;
  return 0;
}
