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


def c(x):
    S=str(x)
    ANS=0
    for s in S:
        ANS+=int(s)

    if ANS<=9:
        return ANS
    else:
        return c(ANS)

x=N+1

import math 
L=math.floor(math.sqrt(x)) # 平方根を求める

Primelist=[i for i in range(x+1)]
Primelist[1]=0 # 1は素数でないので0にする.
 
for i in Primelist:
    if i>L:
        break
    if i==0:
        continue
    for j in range(2*i,x+1,i):
        Primelist[j]=0

Primes=[Primelist[j] for j in range(x+1) if Primelist[j]!=0 and K<=j<=N]

ANS=0
j=0
SET=set()
AX=0
for i in range(len(Primes)):
    while j<len(Primes) and not(c(Primes[j]) in SET):
        SET.add(c(Primes[j]))
        if ANS<=len(SET):
            AX=Primes[i]
            ANS=len(SET)
            
        j+=1
    #print(Primes[i],SET)

    SET.remove(c(Primes[i]))


print(AX)