A, B = input().split()

a = len(A)
b = len(B)
c = 0

if a > b:
	c = A
elif a < b:
	c = B
else:
	for i in range(a):
		if A[i] == '4' and B[i] == '7':
			c = A
			break
		elif A[i] == '7' and B[i] == '4':
			c = B
			break
		elif A[i] > B[i]:
		    c = A
		    break
		elif A[i] < B[i]:
		    c = B
		    break

print(c)