N=int(raw_input())
A=map(int,raw_input().split())
isPrime=[True for i in range(5000001)]
isPrime[0]=False
isPrime[1]=False
primes=[0]
isOK=[False for i in range(10)]
for a in A:
   isOK[a]=True
for i in range(5000001):
   if isPrime[i]:
      primes.append(i)
      for j in range(i+i,5000001,i):
         isPrime[j]=False
primes.append(5000001)
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