from collections import deque

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

prime = []
M = 200001
isPrime = [True]*200001
isPrime[0] = isPrime[1] = False
for i in range(2, M):
  if isPrime[i]:
    prime.append(i)
    for j in range(i*i, M, i):
      isPrime[j] = False

lst = []
for p in prime:
  pp = str(p)
  while len(pp) > 1:
    x = 0
    for v in pp:
      x += int(v)
    pp = str(x)
  lst.append(pp)

dq0 = deque()
dq1 = deque()
max_length = 0
max_values = 0
for p, s in zip(prime, lst):
  if p < K: continue
  if p > N: break
  while dq0 and s in dq0:
    dq0.popleft()
    dq1.popleft()
  dq0.append(s)
  dq1.append(p)
  if max_length <= len(dq0):
    max_length = len(dq0)
    max_values = dq1[0]
print(max_values)