def get_num(s1, s2):

    num = 0

    len_s1 = len(s1)

    list_s1 = []

    for i in range(len_s1):

        two_s1 = s1[0:i+1]

        list_s1.append(two_s1)

    for i in list_s1:

        if s2.startswith(i) and len(i) > num:

            num = len(i)

    return num