def mask_3rd(s):

    ret = ""

    if len(s) < 3:
        return s

    hit = s[2]

    ret = s.replace(hit,"*")

    ret = ret[0:2] + hit + ret[3:]

    return ret

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