a, b = input().split()

if len(a) != len(b):
    print([a, b][int(a) < int(b)])

else:
    c = list(a)
    d = list(b)
    for i in range(len(a)):
        if c[i] == '4' and d[i] == '7':
            c[i] = '9'
        elif c[i] == '7' and d[i] == '4':
            d[i] = '9'
    c = ''.join(c)
    d = ''.join(d)
    print([a, b][int(c) < int(d)])