n = int(input())
A = list(map(int,input().split()))

R = 5000000

sieve = [0]*(R+1)
primes = [0]
for i in range(2,R+1):
    if sieve[i]:
        continue
    primes.append(i)
    for j in range(i,R+1,i):
        sieve[j] = 1
flag = 0
for a in A:
    flag |= 1<<a
ans = -1
now = 1
has = 0
count = [0]*10
l = len(primes)
primes.append(R+2)
for i in range(1,l):
    now = max(now,i)
    while now < l and (has | flag) == flag:
        for j in str(primes[now]):
            j = int(j)
            has |= 1<<j
            count[j] += 1
        now += 1
        if has == flag:
            ans = max(ans,primes[now]-primes[i-1]-2)

    for j in str(primes[i]):
        j = int(j)
        count[j] -= 1
        if count[j] == 0:
            has ^= 1<<j
print(ans)