a, b = map(str,input().split())

if len(a)>len(b):
	print(a)
	exit()

if len(b)>len(a):
	print(b)
	exit()

l = len(a)

for i in range(l):
	if a[i] == b[i]:
		continue
	if a[i] == '4' and b[i] == '7':
		print(a)
		exit()
	if a[i] == '7' and b[i] == '4':
		print(b)
		exit()
	if int(a[i]) > int(b[i]):
		print(a)
		exit()
	if int(b[i]) > int(a[i]):
		print(b)
		exit()