cancel check from checkBox

[24sharon]

I have some checkBox in my page,

I want that the user checked maximum data but no more,

how can I cancel the select option.

here is my code:

protected void CheckBox2_CheckedChanged(object sender, EventArgs e)
    {
        int select = 0;
        int max =3;
        if (max > 0)
        {
            for (int i = 0; i < checkBoxGrid.Items.Count; i++)
            {
                CheckBox cb = (CheckBox)checkBoxGrid.Items[i].FindControl("CheckBox1");
                if (cb.Checked)
                {
                    select++;
                    if (max == select)
                    {
                      //HERE I WANT TO CANCEL
              
                    }
                }
            }
        }
      
    } 

thanks!