a, b = input().split()

if len(a) > len(b):
    print(int(a))
elif len(a) < len(b):
    print(int(b))
else:
    for _, (numa, numb) in enumerate(zip(a, b)):
        if numa == numb:
            continue
        if int(numa) > int(numb):
            if numa == "7" and numb == "4":
                print(int(b))
            else:
                print(int(a))
            exit()
        else:
            if numa == "4" and numb == "7":
                print(int(a))
            else:
                print(int(b))
            exit()