def era(n):
    is_prime = [True]*(n+1)
    is_prime[0] = False
    is_prime[1] = False
    
    for i in range(2, int(n**0.5)+1):
        if not is_prime[i]:
            continue
        
        for j in range(2*i, n+1, i):
            is_prime[j] = False
    
    return [p for p in range(n+1) if is_prime[p]]

N = int(input())
A = list(map(int, input().split()))
S = 0

for Ai in A:
    S += 1<<Ai

p = era(5*10**6)
L = 1
now = 0
ans = -1

for pi in p:
    ok = True
    s = str(pi)
    
    for i in range(len(s)):
        if not (S>>int(s[i]))&1:
            ok = False
            break
    
    if not ok:
        if now==S:
            ans = max(ans, pi-1-L)

        L = pi+1
        now = 0
    else:
        for i in range(len(s)):
            now |= 1<<int(s[i])

if now==S:
    ans = max(ans, 5*10**6-L)

print(ans)