import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

A,B = map(list, read().split())

A = [x - ord('0') for x in A]
B = [x - ord('0') for x in B]

if len(A) > len(B):
    answer = A
elif len(A) < len(B):
    answer = B
else:
    for a,b in zip(A,B):
        if a in [4,7] and b in [4,7]:
            a = 11-a
            b = 11-b
        if a == b:
            continue
        if a > b:
            answer = A
        else:
            answer = B
        break

print(''.join(map(str,answer)))