def mask_3rd(s):

    if len(s) > 4:
        r = s.replace(s[2], "*")
        r = r[:2] + s[2] + r[3:]
        return r
    else:
        return s


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