Sudo Command Unusable

I change my /private/etc permissions to "eveybody can read and write", and applied this permission to all sub-folders and files. (something ****** to do)

After that, when I use "sudo" command something went wrong:

sudo: unable to stat /etc/sudoers: Permission denied

sudo: no valid sudoers sources found, quitting

sudo: unable to initialize policy plugin

Also, I make a change to my "sudoer" file when trying to solve the problem.

Here is its content:

----------------------------------------------------------------------------------------------------------------------------------------

#
# Sample /etc/sudoers file.
#
# This file MUST be edited with the 'visudo' command as root.
#
# See the sudoers man page for the details on how to write a sudoers file.


##
# Override built-in defaults
##
Defaults env_reset
Defaults env_keep += "BLOCKSIZE"
Defaults env_keep += "COLORFGBG COLORTERM"
Defaults env_keep += "__CF_USER_TEXT_ENCODING"
Defaults env_keep += "CHARSET LANG LANGUAGE LC_ALL LC_COLLATE LC_CTYPE"
Defaults env_keep += "LC_MESSAGES LC_MONETARY LC_NUMERIC LC_TIME"
Defaults env_keep += "LINES COLUMNS"
Defaults env_keep += "LSCOLORS"
Defaults env_keep += "SSH_AUTH_SOCK"
Defaults env_keep += "TZ"
Defaults env_keep += "DISPLAY XAUTHORIZATION XAUTHORITY"
Defaults env_keep += "EDITOR VISUAL"
Defaults env_keep += "HOME MAIL"


Defaults lecture_file = "/etc/sudo_lecture"


##
# User alias specification
##
# User_Alias FULLTIMERS = millert, mikef, dowdy


##
# Runas alias specification
##
# Runas_Alias OP = root, operator


##
# Host alias specification
##
# Host_Alias CUNETS = 128.138.0.0/255.255.0.0
# Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
# Host_Alias SERVERS = master, mail, www, ns
# Host_Alias CDROM = orion, perseus, hercules


##
# Cmnd alias specification
##
# Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less


##
# User specification
##


# root and users in group wheel can run anything on any machine as any user
root ALL = (ALL) ALL
%admin ALL = (ALL) ALL


## Read drop-in files from /private/etc/sudoers.d
## (the '#' here does not indicate a comment)
#includedir /private/etc/sudoers.d


[root@localhost ~]# echo 'username  ALL=(ALL)    ALL' >> /etc/sudoer
[root@test ~]# visudo jin ALL=NOPASSWD: ALL




Jin ALL = (ALL) ALL
%wheel        ALL=(ALL)       NOPASSWD: ALL




#includedir /etc/sudoers.d

Can anyone help me?

Thank you.