How To Count Of Characters Entered In Multiline Textbox Till 140 Characters

How to count no. of characters entered in multiline textbox, i wanna enter maximum 140 characters in my multiline textbox using vb.net ...

In short i want textbox to enter limit is only 140 characters ....

i have te following code to do that .... but i wanna implement 140 characters limit in multiline textbox :

<script type="text/javascript">
function Count(x) {
document.getElementById("Label1").innerHTML = document.getElementById("TextBox2").value.length;
}
</script>
<asp:TextBox ID="TextBox2" runat="server" Height="78px"
TextMode="MultiLine" Width="224px" onkeyup="Count(this.id)"
MaxLength="140"></asp:TextBox>