from math import sqrt, ceil


def Sieve(n):
    lst = [True] * (n + 1)
    S = set()
    for i in range(2, ceil(sqrt(n)) + 1):
        if lst[i]:
            for j in range(2 * i, n + 1, i):
                lst[j] = False
    for i in range(2, n + 1):
        if lst[i]:
            S.add(i)
    return lst

N = int(input())
A = set(map(int, input().split()))
M = 5 * 10**6
cnt = 0
Prime = Sieve(M)
S = set()
ans = -1
flag = 0 
Prime[1] = 0
for i in range(1, M + 1):
    if Prime[i]:
        for p in str(i):
            if int(p) not in A:
                S = set()
                cnt, flag = 0, 0
                break
        else:
            cnt += 1
            for p in str(i):
                S.add(int(p))
    else:
        cnt += 1
    
    if S == A:
        flag = 1
    if flag:
        ans = max(ans, cnt - 1) 

print(ans)