from itertools import *
from bisect import *
from math import *
from collections import *
from heapq import *
from random import *
from decimal import *
import numpy as np
import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def MI1(): return map(int1, sys.stdin.readline().split())
def MF(): return map(float, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LF(): return list(map(float, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
dij = [(1, 0), (0, 1), (-1, 0), (0, -1)]

def main():
    def xtobit(x):
        res=0
        for c in str(x):
            res|=1<<int(c)
        return res

    n=II()
    aa=LI()
    a=sum(1<<ak for ak in aa)
    #print(format(a,'b'))

    prime=[0,1]*2500005
    prime[1]=0
    prime[2]=1
    #pp=[]
    l=1
    s=0
    ans=-1
    for x in range(3,5000000):
        #if x**2>5000000:break
        if prime[x]:
            bit=xtobit(x)
            if bit|a!=a:
                if s==a:
                    ans=max(ans,x-l-1)
                    #print(l,x,x-l-1,ans)
                l=x+1
                s=0
            else:
                s|=bit
            #pp.append(x)
            for y in range(x**2,5000001,x*2):
                prime[y]=0
    if s==a:
        ans=max(ans,5000000-l)
    print(ans)

main()