CountClick method for buttons not working
===

I have a few buttons in my webpage and was trying to restrict the button clicks by having a countClick method to check the number of clicks the users have pressed. In my codes below, when users click on the first button, the second button will automatically be clicked for them. And if they were to choose the second button instead, the third button will be clicked for them automatically too and so on for the rest of the buttons. However in my case, they can only click once as one click accounts for 2 buttons to be clicked. So, when they have clicked once, i cannot allow them to click on the second time. 

My problem is that my countClick method is not working. When i run my page, all my buttons can be selected and it does not restrict the user to only 1 button click.

Here is my .cs code:

    protected void Button1_Click(object sender, EventArgs e)
    {
        Button1.Text = "Booked";
        Button1.BackColor = System.Drawing.Color.Blue;
        Button2.Text = "Booked";
        Button2.BackColor = System.Drawing.Color.Blue;
        countClick();
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        Button2.Text = "Booked";
        Button2.BackColor = System.Drawing.Color.Blue;
        Button3.Text = "Booked";
        Button3.BackColor = System.Drawing.Color.Blue;
        countClick();
    }
    protected void Button3_Click(object sender, EventArgs e)
    {
        Button3.Text = "Booked";
        Button3.BackColor = System.Drawing.Color.Blue;
        Button4.Text = "Booked";
        Button4.BackColor = System.Drawing.Color.Blue;
        countClick();
    }
    protected void Button4_Click(object sender, EventArgs e)
    {
        Button4.Text = "Booked";
        Button4.BackColor = System.Drawing.Color.Blue;
        countClick();
    }


Here is my countClick method in .cs:

    private void countButtonClick()
    {
        int counter = 0;
        counter++;
        if (counter >= 1)
        {
            Response.Write("You can only select 2 slots! " + DateTime.Now.ToString());
        }
    }