#python -m pdb a.py

B=25*10**6
P=[]
C=[0]*B
for i in range(2,B):
	if C[i]<1:
		P+=[i];j=i*i
		while j<B:C[j],j=1,j+i
length=len(P)

import random
Q=[2,3,5,7,11,13,17,19,23,29]
def MillerRabin(n,Q):
	assert n>0
	if n<2:return 0
	if n in Q:return 1
	if any(n%p<1 for p in Q):return 0
	for t in range(10):Q+=[random.randint(30,n-1)]
	u,v=n-1,0
	while u&1<1:u>>=1;v+=1
	for p in Q:
		m=pow(p,u,n)
		if m!=1:
			for e in range(v):
				if m==n-1:break
				m=m*m%n
			else:return 0
	return 1

J=lambda:list(map(int,input().split()))
L,R=J()

for i in range( 1 , length - 2 ):
	a2 = P[i] * P[i];
	if( a2 * P[i+1] * P[i+2] > R ):
		 break;
	for j in range( i + 1 , length - 1 ):
		a2b = a2 * P[j]
		a2bc = a2b * P[j+1]
		if( a2bc > R ):
			break;
		a2bc = a2b * P[length - 1]
		if( a2bc < L ):
			c_min = ( ( L + a2b - 1 ) // a2b ) | 1
			c_max = R // a2b;
			assert( c_min > P[length-1] );
			for c in range( c_min , c_max + 1 , 2 ):
				if( MillerRabin( c , Q ) ):
					exit( print( a2b * c ) );
		else: 
			l,r=j,length-1
			while l+1<r:
				m=(l+r)>>1
				if( a2b * P[m] < L ):l=m
				else:r=m
			a2bc = a2b * P[r];
			if( L <= a2bc <= R ):
				exit( print( a2bc ) );
print( -1 );