def make_prime(n):
    prime = [True] * (n + 1)
    prime[0] = False
    prime[1] = False
    
    for i in range(2, n + 1):
        if prime[i]:
            for j in range(i * 2, n + 1, i):
                prime[j] = False
    return prime

def digit(x):
    if not isprime[x]:
        return 0
    
    d = 0
    while x > 0:
        d |= (1 << (x % 10))
        x //= 10
        
    return d
        
if __name__ == '__main__':
    N = int(input())
    A = list(map(int, input().split()))
    
    e = 0
    for x in A:
        e ^= (1 << x)
        
    isprime = make_prime(5000000)
    
    data = [digit(i) for i in range(len(isprime))]
    
    result = -1
    r = 0
    s = 0
    for l, x in enumerate(data):
        if (x | e) == e:
            s |= x
            continue
        if s == e:
            result = max(result, l - r  - 2)
        r = l
        s = 0
        
    if s == e:
        result = max(result, len(isprime) - r - 2)

    print(result)