marked as override cannot be marked as new or virtual

[petitdede]

Hello,
i have do do an exercise,
but i have always an error like"marked as override cannot be marked as new or virtual"
my program is:

public class Shape
 
{
    protected Point p;
    public Point my_p
    {get; set;}
    public Shape (){}
    public Shape(Point p) { this.p = new Point(p.my_x, p.my_y); }
    public virtual void Show() { p.Show(); }
}
 
 
public class Segment :Shape
{
 
   protected int a;
 
   public int my_a { get; set; }
   public Segment() :base(new Point(0,0))
   {this.a = 0; }
 
    public Segment(Point p, int a):base(p)
    { this.a = a; }
    public override void Show()
    {
        Console.WriteLine("Segment Point ");
        p.Show();
        Console.WriteLine("Length ",a);
 
    }
}
 
 
 
public class RealPoint : Segment
{
 
 
    public RealPoint(Point p)
        : base(p, 0) {}
    public  override void Show()
 { Console.WriteLine("RealPoint Point "); p.Show();}
 
}
 
 
 
 
using System;
   public class Point
    {
      public int x;
  public int y;
    public Point() { x = 0; y = 0; }
    public Point(int x,int y) { this.x = x; this.y = y; }
    public Point(Point p) { this.x = p.my_x; this.y = p.my_y; }
 
    public int my_x { get { return x; } set {  x = value; } }
    public int my_y { get { return y; } set {  y = value; } }
        public static Point operator +(Point p1, Point p2)
        {
            Point ret = new Point(p1.x + p2.x, p1.y + p2.y);
            return ret;
        }
        public static Point operator -(Point p1, Point p2)
        {
            Point ret = new Point(p1.x - p2.x, p1.y - p2.y);
            return ret;
 
        }
        public static Point operator +(Point p1, Size s)
        {
            Point ret = new Point(  p1.x + (int)s.my_x,p1.y + (int)s.my_y);
 
 
            return ret;
 
        }
 
        public void Show(){
 
           Console.WriteLine("(",x,",",y,")");
 
       }
 
    }
 
 
 
 
public class Size
{
    public uint x;
    public uint y;
    public Size() { x = 0; y = 0; }
    public Size(uint x,uint y) {this.x = x; this.y = y; }
    public uint my_x { get { return x; } set { if (value >= 0) x = value; } }
    public uint my_y { get { return y; } set { if (value >= 0) y = value; } }
     public static Size operator +(Size s, Point p1)
    {
     Size ret = new Size();
        return ret;
 
     }
 
         public void Show()
        {
 
            Console.WriteLine("(", x, ",", y, ")");
 
        }
}

I have blue marks in the show function with the above error (marked as override cannot be marked as new or virtual)

thank for asnwer