K = int(input())
N = int(input())

dat = [0] * (N + 1)
prime = []
for i in range(2,N+1):
    if dat[i] == 0:
        for j in range(i * 2,N+1,i):
            dat[j] = 1
        if i >= K:
            prime.append(i)
def hash(x):
    if x <= 9:return x
    a = 0
    while x:
        a += x % 10
        x //= 10
    return hash(a)
N = len(prime)
right = 0
s = set()
_max = 0
index = -1
for left in range(N):
    while right < N and hash(prime[right]) not in s:
        s.add(hash(prime[right]))
        right += 1
    if right - left >= _max:
        _max = right - left
        index = prime[left]
    s.remove(hash(prime[left]))
print(index)