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 = []

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)

max = 0
max_len = 0
for i in range(len(primes)):
    col = []
    for p in primes[i:]:
        x = sp(p)
        if x in col:
            break
        else:
            col.append(x)
    if max_len <= len(col):
        max_len = len(col)
        if max < primes[i]:
            max = primes[i]

print(max)