k = int(input())
n = int(input())

primes = []
l = []
for i in range(2,n+1):
    check = True
    for p in primes:
        if p**2 > i:
            break
        if i%p == 0:
            check = False
            break
    if check:
        primes.append(i)
        if k <= i <= n:
            l.append(i)

def hash(x):
    now = x
    while True:
        now = sum([int(i) for i in str(now)])
        if now < 10:
            return now

count = [0]*10
now = 0
ans = []
hashl = [hash(i) for i in l]

for i,h in enumerate(hashl):
    while now < len(l) and count[hashl[now]] == 0:
        count[hashl[now]] += 1
        now += 1
    ans.append(now-i)
    count[hashl[i]] -= 1
m = max(ans)
for i in range(len(ans))[::-1]:
    if ans[i] == m:
        print(l[i])
        exit()