L, R = map(int, input().split())
if R - L >= 45000:
    R = L + 45000

divs = [[] for _ in range(R - L + 1)]
now = [i + L for i in range(R - L + 1)]

isprime = [True for _ in range(23000001)]
for i in range(2, 23000001):
    if isprime[i]:
        for j in range(2, 23000000 // i + 1):
            isprime[j * i] = False

for i in range(2, 23000001):
    min_v = ((L + i - 1) // i) * i
    for j in range(min_v, R + 1, i):
        while now[j - L] % i == 0:
            now[j - L] //= i
            divs[j - L].append(i)

for j in range(R - L + 1):
    if now[j] != 1:
        divs[j].append(now[j])

for j in range(R - L + 1):
    if len(divs[j]) != 4:
        continue
    if divs[j][0] == divs[j][1] and divs[j][1] != divs[j][2] and divs[j][2] != divs[j][3] and divs[j][0] != 2:
        print(L + j)
        exit()
print(-1)