def mask_3rd(word):
    if len(word) < 3:
        return word
    else:
        ch = word[2]
        ret = word.replace(ch, "*")
        return "".join([ret[:2], ch, ret[3:]])

print(mask_3rd('logging'))
print(mask_3rd('apple'))
print(mask_3rd('orange'))
print(mask_3rd('gooooogle'))
print(mask_3rd('i'))