a,b=raw_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