M = 22500000

f = [0 for i in range(M + 1)]
prime = [0 for i in range(M + 1)]
for x in range(2, M + 1):
	f[x] = x
for x in range(2, M + 1):
	if f[x] != 1:
		prime[x] = 1
		y = 2 * x
		while y <= M:
			while f[y] % x == 0:
				f[y] //= x;
			y += x

l, r = map(int, input().split())

if r - l >= 45000:
	r = l + 45000

g = [0 for i in range(r - l + 1)]
h = [[] for i in range(r - l + 1)]

for x in range(l, r + 1):
	g[x - l] = x

for x in range(2, M + 1):
	if prime[x]:
		start = (l + (x - 1)) // x * x
		end = r // x * x
		y = start
		while y <= end:
			while g[y - l] % x == 0:
				g[y - l] //= x;
				h[y - l].append(x)
			y += x

for x in range(l, r + 1):
	if g[x - l] != 1:
		h[x - l].append(g[x - l])
	
ans = -1
for x in range(l, r + 1):
	if len(h[x - l]) == 4:
		if h[x - l][0] == h[x - l][1] and h[x - l][1] != h[x - l][2] and h[x - l][2] != h[x - l][3]:
			ans = x

print(ans)