from copy import copy

def prime_num(end):
    prime_list = [True for i in range(end + 1)]
    prime_list[0], prime_list[1] = False, False
    
    for i in range(2, int(end ** 0.5) + 1):
        if not prime_list[i]:
            continue
        for j in range(i * 2, end + 1, i):
            prime_list[j] = False
            
    return (i for i in range(2, end + 1) if prime_list[i])
            
N = int(input())
A = set(input().split())
ans = -1

prime = prime_num(5 * 10 ** 6)
lists = copy(A)
left = 1
right = 1
nokori = copy(A)

for i in prime:
    right = i - 1
    tmp = set(str(i))
    if A | tmp != A:
        if nokori:
            left = i + 1
            nokori = copy(A)
            continue
        else:
            ans = max(ans, abs(right - left))
            nokori = copy(A)
            continue
    nokori = nokori - tmp
    
print(ans if len(A) != 10 else 4999999)