import heapq
from collections import deque
import re

def sp(p):
    v = str(p)
    while v:
        s = 0
        for vv in v:
            s += int(vv)
        if s < 10:
            return int(s)
        v = str(s)

K = int(input())
N = int(input())
primes = []
hashes = []

if K < 2:
    K = 2

for i in range(K, N + 1):
    for j in range(2, i):
        if i % j == 0:
            break
    else:
        primes.append(i)
        hashes.append(sp(i))

start = 0
end = 0
coll = deque()
mx = []
while(start <= end < len(hashes)):
    if hashes[end] not in coll:
        coll.append(hashes[end])
        end += 1
    else:
        heapq.heappush(mx, [-(len(coll)), -(primes[start])])
        coll.clear()
        start += 1
        end = start

heapq.heappush(mx, [-(len(coll)), -(primes[start])])
print(-(heapq.heappop(mx)[1]))