A, B = input().split()

La, Lb = len(A), len(B)

if La > Lb:
	print (A)

elif La < Lb:
	print (B)

else:
	for i in range(La):
		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