N=int(raw_input())
A=map(int,raw_input().split())

isOK=[False for i in range(10)]
for a in A:
   isOK[a]=True


upperBound = 5000001
isPrime=[True for i in range((upperBound-3)/2+1)]
for i in range((upperBound-3)/2+1):
   if isPrime[i]:
      k = i+i+3 # this is prime number
      # false out non_prime number
      # k*k = 4i^2+12i+9 = 2*(2i^2+6i+3)+3
      # k*(k+1) = 2*(2i^2+6i+3)+3 + 2i+3 ... even number. skip
      # k*(k+2) = 2*(2i^2+6i+3+k)+3 
      non_prime = k*(i+1)+i
      for j in range(non_prime,(upperBound-3)/2+1,k):
         isPrime[j]=False
primes = [2] + [i+i+3 for i in range((upperBound-3)/2+1) if isPrime[i]==True]
primes = [0]+primes+[upperBound]
#print len(primes)
ans = -1
i = 1
while i < len(primes)-1:
   p=primes[i]
   ok=True
   s= set([])
   #print primes[i]
   while p != 0:
      if isOK[p%10] == False :
         ok=False
         break
      s.add(p%10)
      p/=10
   if ok==False:
      i+=1
      continue
   j = i+1
   while j < len(primes)-1:
      p = primes[j]
      ok2=True
      while p != 0:
         if isOK[p%10] == False:
            ok2=False
            break
         p/=10
      if ok2== False:
         break
      p=primes[j]
      while p != 0:
         s.add(p%10)
         p/=10
      j+=1
   if len(s)==N:
      ans = max(ans, primes[j]-1-(primes[i-1]+1) )
   #print primes[i-1],primes[j]
   i=j+1
print ans