#!/usr/bin/env python3
import operator
from collections import defaultdict
from functools import lru_cache, reduce
from itertools import dropwhile, takewhile


def sqrt_floor(n):
    l = 5 * n
    r = 5
    sqrt = 0
    while l > r:
        sqrt += 1
        l = l - r
        r += 10
    return sqrt


def sieve_of_eratosthenes(max):
    is_prime = [True] * (max + 1)
    is_prime[0] = False
    is_prime[1] = False
    for i in range(2, sqrt_floor(max) + 1):
        if not is_prime[i]:
            continue
        for j in range(i * i, max + 1, i):
            is_prime[j] = False
    return filter(lambda x: is_prime[x], range(max + 1))


def set_of_nums(n):
    return frozenset(list(str(n)))

PRIME = [1] + list(sieve_of_eratosthenes(5000000))
PRIME_NUMS = tuple(map(set_of_nums, PRIME))
N = int(input())
A = frozenset(input().split())
maxdistance = -1
count = 0
now = set()
from_one = True
for i in range(len(PRIME_NUMS)):
    if PRIME_NUMS[i] <= A:
        now.update(PRIME_NUMS[i])
        count += 1
        continue
    if now == A:
        maxdistance = max(maxdistance, PRIME[i] - PRIME[i - count - 1] - 2)
    count = 0
    now = set()
    from_one = False
if now == A:
    if from_one:
        maxdistance = max(maxdistance, 5000000 - 1)
    else:
        maxdistance = max(maxdistance, 5000000 - PRIME[i - count - 1] - 2)
print(maxdistance)