c# make form draggable

private bool mouseDown;
private Point lastLocation;

    private void Form1_MouseDown(object sender, MouseEventArgs e)
    {
        mouseDown = true;
        lastLocation = e.Location;
    }

    private void Form1_MouseMove(object sender, MouseEventArgs e)
    {
        if(mouseDown)
        {
            this.Location = new Point(
                (this.Location.X - lastLocation.X) + e.X, (this.Location.Y - lastLocation.Y) + e.Y);

            this.Update();
        }
    }

    private void Form1_MouseUp(object sender, MouseEventArgs e)
    {
        mouseDown = false;
    }

[DllImport("user32")]
private static extern bool ReleaseCapture();

[DllImport("user32")]
private static extern int SendMessage(IntPtr hWnd, int Msg, int wp, int lp);

protected override void OnMouseDown(MouseEventArgs e)
{
  	base.OnMouseDown(e);
	if (e.Button == MouseButtons.Left)
    {
    	ReleaseCapture();
      	SendMessage(Handle, 161, 2, 0);
    }
}