Drawing a line between two points with Mouseclick

Question

Hello everyone

I'm trying to make a very basic dwawing application where you can draw (eg. a line) on a panel. 

The very basic code to draw a line on the panel by code is this:

       private void panel1_Paint(object sender, System.Windows.Forms.PaintEventArgs e)

        {

            Pen blackPen = new Pen(Color.Black, 4);

            int X1 = 0, Y1 = 0, X2 = 250, Y2 = 100;

            Graphics graphics = panel1.CreateGraphics();

            e.Graphics.DrawLine(blackPen, X1, Y1, X2, Y2);

            blackPen.Dispose();

        }

Now is my question: how do i have to write the code so i can draw a line with 2 mouseclicks? 

I think we could use point structures ? But how do i have to write everything ?