import sys
import math as mas

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]!=b[i]:
			if max(a[i],b[i])=="7" and min(a[i],b[i])=="4":print(min(a,b))
			else:print(max(a,b))
			break

#for i in sys.stdin:
#	a,b=map(int,i.split())
#	print(gcd(a,b),lcm(a,b))