def decode(s):
    """
    Converts text in the numbering format of pinyin ("ni3hao3") to text with the 
    appropriate tone marks ("nǐhǎo").
    """

    s = s.lower()
    r = ""
    t = ""
    for c in s:
        if c >= 'a' and c <= 'z':
            t += c
        elif c == ':':
            try:
                if t[-1] == 'u':
                    t = t[:-1] + u"\u00fc"
            except:
                pass
        else:
            if c >= '0' and c <= '5':
                tone = int(c) % 5
                if tone != 0:
                    m = re.search(u"[aoeiuv\u00fc]+", t)
                    if m is None:
                        t += c
                    elif len(m.group(0)) == 1:
                        t = t[:m.start(0)] + PinyinToneMark[tone][PinyinToneMark[0].index(m.group(0))] + t[m.end(0):]
                    else:
                        if 'a' in t:
                            t = t.replace("a", PinyinToneMark[tone][0])
                        elif 'o' in t:
                            t = t.replace("o", PinyinToneMark[tone][1])
                        elif 'e' in t:
                            t = t.replace("e", PinyinToneMark[tone][2])
                        elif t.endswith("ui"):
                            t = t.replace("i", PinyinToneMark[tone][3])
                        elif t.endswith("iu"):
                            t = t.replace("u", PinyinToneMark[tone][4])
                        else:
                            t += "!"
            r += t
            t = ""
    r += t
    return r