K=int(input())
N=int(input())

l=N+1
P=[1]*l
for i in range(2,l):
  if P[i]:
    for j in range(i+i,l,i):
      P[j]=0
P=[i for i in range(2,l) if P[i] and K<=i<=N]

def HASH(x):
  if x<10:
    return x
  return HASH(sum(list(map(int,str(x)))))

a=(0,0)
for w in range(1,10):
  for l in range(len(P)-w+1):
    r=l+w-1
    if len(set([HASH(i) for i in P[l:r+1]]))==w:
      a=max(a,(w,P[l]))

print(a[1])