K=int(raw_input())
N=int(raw_input())
isPrime=[True for i in range(N+1)]
isPrime[0]=False
isPrime[1]=False
primes=[]
for i in range(N+1):
   if isPrime[i]:
      for j in range(i+i,N+1,i):
         isPrime[j]=False
      if i>=K and i <=N:
         primes.append(i)
hashs=[]
for p in primes:
   while p>=10:
      q = 0
      while p!=0:
         q+=p%10
         p/=10
      p=q
   hashs.append(p)

maxLen=0
ans = 2
for i in range(len(primes)):
   isUsed=[False for k in range(10)]
   curLen=0
   j = i
   while j<len(primes) and isUsed[hashs[j]]== False:
      isUsed[hashs[j]]=True
      curLen+=1
      j+=1
   if maxLen <= curLen:
      maxLen = curLen
      ans = primes[i]
print ans