[Javascript] Auto deleselecting a check box

[DEV]

Say you have a question like this ?

Which countries have you been so far ?

USA
UK
MEXICO
TELL YOU LATER ( pre checked )

When user selects USA/UK and/or MEXICO, the pre-checked [tell you later]
option should be unchecked. How do you accomplish this ?

<input type=checkbox name=countriesbeen value='USA'
onClick='UnCheckTellYouLater()'>USA
<input type=checkbox name=countriesbeen value='UK'
onClick='UnCheckTellYouLater()'>UK
<input type=checkbox name=countriesbeen value='MEXICO'
onClick='UnCheckTellYouLater()'>MEXICO
<input type=checkbox name=countriesbeen value='Tell you later'
onClick='UnCheckTellYouLater()'>Tell you later


function UnCheckTellYouLater()
    //what do you do here to UnCheck Tell You Later
end function