#!/usr/bin/python2
# -*- coding: utf-8 -*-
# †
from itertools import permutations
from random import randrange

def memoize(func):
    cache = {}
    def _memoizer(*args):
        res = cache.get(args)
        if res == None:
            res = cache[args] = func(*args)
        return res
    _memoizer.cache = cache
    return _memoizer

@memoize
def is_probable_prime(n, k=20):
    if n == 1: return False
    for p in [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31]:
        if n == p:     return True
        if n % p == 0: return False
    s, d = 0, n-1
    while d & 1 == 0:
        s, d = s+1, d>>1
    for _ in xrange(k):
        a = randrange(2, n-1)
        x = pow(a, d, n)
        if x == 1 or x == n-1:
            continue
        for _ in xrange(s-1):
            x = x * x % n
            if x == n-1:
                break  # could be strong liar, try another a
        else:
            return False  # composite if we reached end of this loop
    return True  # probably prime if reached end of outer loop

n = int(raw_input())
v = map(int, raw_input().split())

maxi = -1
for perm in permutations(v):
    x = int(''.join(map(str, perm)))
    if maxi < x and is_probable_prime(x):
        maxi = x
print maxi