# ref http://yukicoder.me/submissions/3957
import math

def prime(max):
    max2 = (max-3)//2
    sieve = [True]*(max2+1)
    for i in range(int((math.sqrt(max)-3)/2)+1):
        if not sieve[i]: continue
        k = i+i+3
        j = k*(i+1)+i
        while j <= max2:
            sieve[j] = False
            j += k
    sieve = [2]+[i+i+3 for i in range(max2+1) if sieve[i]]
    return sieve


input()
a=set(input().split())

max=5000000
start=1
rest=a
ans=-1
for i in prime(max):
  l=set(str(i))
  if len(l-a):
    if len(rest)==0 and ans<i-1-start: ans=i-1-start
    start=i+1
    rest=a
  else:
    rest=rest-l
if len(rest)==0 and ans<max-start: ans=max-start
print(ans)