#include <bits/stdc++.h>
#include <assert.h>

using namespace std;

long long powMod(long long x, long long k, long long m)
{
  if (k == 0)
    return 1;
  if (k % 2 == 0)
    return powMod(x * x % m, k / 2, m);
  else
    return x * powMod(x, k - 1, m) % m;
}

bool suspect(long long a, int s, long long d, long long n)
{
  long long x = powMod(a, d, n);
  if (x == 1)
    return true;
  for (int r = 0; r < s; ++r)
  {
    if (x == n - 1)
      return true;
    x = x * x % n;
  }
  return false;
}
// {2,7,61,-1}                 is for n < 4759123141 (= 2^32)
// {2,3,5,7,11,13,17,19,23,-1} is for n < 10^16 (at least)
bool isPrime(long long n)
{
  if (n <= 1 || (n > 2 && n % 2 == 0))
    return false;
  int test[] = {2, 3, 5, 7, 11, 13, 17, 19, 23, -1};
  long long d = n - 1, s = 0;
  while (d % 2 == 0)
    ++s, d /= 2;
  for (int i = 0; test[i] < n && test[i] != -1; ++i)
    if (!suspect(test[i], s, d, n))
      return false;
  return true;
}

int main()
{
  int n;
  cin >> n;
  vector<string> a(n);
  for (int i = 0; i < n; i++)
    cin >> a[i];
  sort(a.begin(), a.end());
  long long ans = 0;
  do
  {
    string tmp;
    for (int i = 0; i < n; i++)
      tmp += a[i];
    long long check = stoll(tmp);
    cerr << check << endl;
    if (isPrime(check))
      ans = max(ans, check);
  } while (next_permutation(a.begin(), a.end()));
  cout << (ans == 0 ? -1 : ans) << endl;

  return 0;
}