#include <bits/stdc++.h>
using namespace std;
int n, m;
int a[233], b[233];
long long gena[2333333], genb[2333333];
int topa, topb;
long long k;
void search(int *arr, long long *gen, int &top, long long cur, int dep) {
  if (arr[dep] == 0) {
    gen[++top] = cur;
    return;
  }
  search(arr, gen, top, cur, dep + 1);
  while (cur <= 1000000000000000000ll / arr[dep] + 1) {
    cur *= arr[dep];
    if (cur <= 1000000000000000000ll) search(arr, gen, top, cur, dep + 1);
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    if (i & 1)
      scanf("%d", &a[i / 2 + 1]);
    else
      scanf("%d", &b[i / 2]);
  }
  scanf("%lld", &k);
  search(a, gena, topa, 1, 1);
  search(b, genb, topb, 1, 1);
  sort(gena + 1, gena + topa + 1);
  sort(genb + 1, genb + topb + 1);
  long long l = 1, r = 1000000000000000000ll, cnt;
  while (l < r) {
    long long mid = (l + r) >> 1;
    cnt = 0;
    int p = topb;
    for (int i = 1; i <= topa; i++) {
      while (p > 0 &&
             (gena[i] > mid / genb[p] + 1 || gena[i] * genb[p] > mid)) {
        p--;
      }
      cnt += p;
    }
    if (cnt >= k)
      r = mid;
    else
      l = mid + 1;
  }
  printf("%lld\n", l);
  return 0;
}
