a, b = map(str, 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 int(a[i]) > int(b[i]):
            print(a)
            break
        elif int(a[i])<int(b[i]):
            print(b)
            break