private void pictureBox1_Paint(object sender, PaintEventArgs e)
        {
            if (touchPoint != -1 && touch)
            {
                e.Graphics.DrawEllipse(penPoints, list[touchPoint].X - 5, list[touchPoint].Y - 5, 10, 10);
            }
        }

        private void pictureBox_mouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                for (int i = 0; i < list.Count; i++)
                    {
                        if ((e.X - list[i].X) * (e.X - list[i].X) + (e.Y - list[i].Y) * (e.Y - list[i].Y) <= 400f)
                        {
                            touchPoint = i;
                            touch = true;
                            break;
                        }
                    }
                if (!touch)
                {
                    list.Add(new Point(e.X, e.Y));
                }
            }
            pictureBox1.Invalidate();
        }
        private void pictureBox_mouseMove(object sendre, MouseEventArgs e)
        {
            if (touch)
            {
                list[touchPoint] = new Point(e.X, e.Y);
                pictureBox1.Invalidate();
            }
        }
        private void pictureBox_mouseUp(object sender, MouseEventArgs e)
        {
            if (touch)
            {
                list[touchPoint] = new Point(e.X, e.Y);
                touch = false;
            }
        }