A,B = input().split()
if len(A) > len(B):
	print (A)
elif len(A) < len(B):
	print (B)
else:
	for i in range(len(A)):
		if A[i] == '4' and B[i] == '7':
			print (A)
			break
		elif A[i] == '7' and B[i] == '4':
			print (B)
			break
		elif A[i] < B[i]:
			print (B)
			break
		elif A[i] > B[i]:
			print (A)
			break