import std.algorithm, std.array, std.container, std.range, std.bitmanip;
import std.numeric, std.math, std.bigint, std.random;
import std.string, std.conv, std.stdio, std.typecons;

const auto maxPeriod = 5000000;

void main()
{
  auto n = readln.chomp.to!int;
  auto ai = readln.split.map!(to!int);

  auto b = 0;
  foreach (a; ai) b |= (1 << a);

  auto pi = primes(maxPeriod);
  auto qi = pi.map!(digits);

  auto maxLen = 0;
  auto s = -1;
  foreach (t, p; pi) {
    if ((qi[t] & ~b) != 0) {
      if (s != -1 && qi[s..t].reduce!("a | b") == b) {
        auto p1 = s == 0 ? 1 : pi[s - 1] + 1;
        auto p2 = t == pi.length - 1 ? maxPeriod : pi[t] - 1;
        auto len = p2 - p1;
        maxLen = max(maxLen, len);
      }
      s = -1;
    } else {
      if (s == -1)
        s = t.to!int;
    }
  }
  if (s != -1) {
    auto t = pi.length;
    auto p1 = s == 0 ? 1 : pi[s - 1] + 1;
    auto p2 = maxPeriod;
    auto len = p2 - p1;
    maxLen = max(maxLen, len);
  }

  writeln(maxLen == 0 ? -1 : maxLen);
}

int digits(int n)
{
  auto r = 0;
  for (; n > 0; n /= 10) r |= (1 << (n % 10));
  return r;
}

int[] primes(int n)
{
  auto sieve = new bool[](n + 1);
  sieve[0..2] = false;
  sieve[2..$] = true;

  foreach (p; 2..n.to!real.sqrt.to!int + 1)
    if (sieve[p])
      foreach (q; iota(p * 2, n + 1, p))
        sieve[q] = false;

  return sieve.enumerate
    .filter!("a[1]")
    .map!("a[0]").map!(to!int).array;
}