def sieve(n):
    is_prime = [True] * (n+1)
    is_prime[0] = is_prime[1] = False
    for j in range(4, n+1, 2):
        is_prime[j] = False
    prime = [2]
    for i in range(3, n+1):
        if is_prime[i]:
            prime.append(i)
            for j in range(i*i, n+1, 2*i):
                is_prime[j] = False
    return prime

M = 5*10**6
prime = [0] + sieve(M) + [M+1]
N = int(input())
A = set(map(int, input().split()))
st = set()
ans = -1
left = 0
for i, p in enumerate(prime):
    if i == 0 or i == len(prime) - 1:
        continue
    for d in map(int, str(p)):
        if d not in A:
            st = set()
            left = i
            break
        st.add(d)
    else:
        if st == A:
            ans = max(ans, prime[i + 1] - prime[left] - 2)
print(ans)