#!/usr/bin/env python3
# -*- coding: utf-8-*-
import math

def h(n):
    r = n%10
    while n >= 10:
        n //= 10
        r += n%10
    if r >= 10:
        r = h(r)
    return r

def isp(n):
    if n == 1:
        return False
    for i in range(2, math.floor(math.sqrt(n))+1):
        if n % i == 0:
            return False
    return True

if __name__ == '__main__':
    k = int(input())
    n = int(input())
    l = [-1,-1,-1,-1,-1,-1,-1,-1,-1,-1]
    p = []
    s = 0
    a = 0
    ap = 2
    ii = 0
    for i in range(k, n+1):
        if isp(i):
            p.append(i)
            ha = h(i)
            if l[ha] != -1:
                if s <= l[ha]:
                    d = ii - s
                    if a <= d:
                        a = d
                        ap = p[s]
                    s = l[ha]+1
            l[ha] = ii
            ii += 1
    d = len(p) - s
    if a <= d:
        a = d
        ap = p[s]
    print(ap)