# -*- coding: utf-8 -*-
"""
Created on Sat Jul  6 09:36:27 2019

@author: Jiang.Lijin
"""

def mask_3rd(s):
    #3以下そのまま返す
    if len(s) <= 3:
        return s

    #置換
    ret = s.replace(s[2], "*")
    #返す文字列結合
    return ret[:2] + s[2] + ret[3:]

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