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


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