#yuki_12

def primes(n): 
 if n==2: return [2]
 elif n<2: return []
 s=range(3,n+1,2)
 mroot = n ** 0.5
 half=(n+1)/2-1
 i=0
 m=3
 while m <= mroot:
  if s[i]:
   j=(m*m-3)/2
   s[j]=0
   while j<half:
    s[j]=0
    j+=m
  i=i+1
  m=2*i+3
 return [2]+[x for x in s if x]

raw_input()
a=set(raw_input().split())
res=-1
l=1
cnt=0
s=set()
for i in primes(5000000):
 ts=set(str(i))
 if len(ts-a)>0:
  if cnt>0 and len(s)==len(a):
   res=max(res,i-1-l)
  l=i+1
  cnt=0
  s=set()
 else:
  s=s.union(set(str(i)))
  cnt+=1
if cnt>0 and len(s)==len(a):
 res=max(res,5000000-l)
print res