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