list the names of users who logoff in last 4 minutes

i am new to unix shell program,
please someone hint me how to get the names of users who make logouts in last 4 minutes?
i dont need complete script, but only the guide

Use the "last" command. This will list who logged in and out. From there you can grep the 7th coloum for a time that is 4 minutes less than you current time....

thnak you very much