from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline


K = int(input())
N = int(input())
class pf():
    
    def __init__(self,M=10**6):
        self.sieve = [-1]*(M+1)
        self.sieve[1] = 1
        self.p = [False]*(M+1)
        for i in range(2,M+1):
            if self.sieve[i] == -1:
                self.p[i] = True
                for j in range(i,M+1,i):
                    self.sieve[j] = i
                    
    def factors(self,x):
        tmp = []
        while self.sieve[x] != x:
            tmp.append(self.sieve[x])
            x //= self.sieve[x]
        tmp.append(self.sieve[x])
        return tmp
        
    def is_prime(self,x):
        return self.p[x]
        
P = pf()
X = []
for i in range(K,N+1):
    if P.is_prime(i):
        X.append(i)

def hash(x):
    
    tx = x
    while len(str(tx))!=1:
        tx = sum(int(i) for i in list(str(tx)))
        
    return tx

    
Y = [hash(x) for x in X]
n = len(X)

ans = -1
M = -1
delta = min(n,10)

for d in range(1,delta+1):
    
    for i in range(n-d+1):
        
        if len(set(Y[i:i+d]))==d:
            M = X[i]
print(M)