k=int(input())
n=int(input())
a=list(range(n+1))
a[1]=0
count=2
while count**2<=n:
    i=2
    while count*i<=n:
        a[count*i]=0
        i+=1
    count+=1
list=[]
sum_list=[]

def fun(num):
    while int(num)>=10:
        sum=0
        for i in range(len(str(num))):
            sum+=int(str(num)[i])
        num=sum
    return num

for i in a:
    if k<=i and i<=n and i>0:
        list.append(fun(i))
        sum_list.append(i)


dp=[False]*10
max=0
sum=0
for i in range(len(list)):
    dp = [False] * 10
    count=0
    dp[list[i]]=True
    for j in range(i+1,len(list)):
        if dp[list[j]]:
            if max<=count:
                sum=sum_list[i]
                max=count
            break;
        dp[list[j]]=True
        count+=1
    if max <= count:
        sum = sum_list[i]
        max = count

print(sum)