IsPrime = [True for _ in range(5 * 10**6 + 1)]
Primes = []
IsPrime[0] = IsPrime[1] = False
for i in range(2, 5 * 10**6 + 1):
    if IsPrime[i]:
        Primes.append(i)
        for j in range(i * i, 5 * 10**6 + 1, i):
            IsPrime[j] = False
m = len(Primes)

n = int(input())
use_set = set(map(int, input().split()))
used_set = set()
l = 1
ans = -1
for idx in range(m):
    prime = Primes[idx]
    prime_s = str(prime)
    flag = True
    for d in prime_s:
        if int(d) not in use_set:
            flag = False
            if used_set == use_set:
                ans = max(ans, prime - 1 - l)
            l = prime + 1
            used_set = set()
            break
    if flag:
        for d in prime_s:
            used_set.add(int(d))
    if used_set == use_set:
        ans = max(ans, prime - l)
if used_set == use_set:
    ans = max(ans, 5 * 10**6 - l)
print(ans)