s = set(['4','7'])
def less(x,y):
	if x == y:
		return False
	if x in s and y in s:
		return x == '7'
	else:
		return x < y
A,B = raw_input().split()
a = len(A)
b = len(B)
if a > b:
	print A
elif a < b:
	print B
else:
	for i in xrange(a):
		if less(A[i],B[i]):
			print B
			break
		elif less(B[i],A[i]):
			print A
			break
	else:
		print A