uses graph,crt ;
var d,m,x,y: integer;
  begin
  d:=detect; initgraph(d,m,' ');


  setcolor(blue);
     line(40,40,40,340);
     line(40,340,340,340);
     line(340,340,40,40);
    x:=40;
    y:=40;
   setcolor(15);
  repeat

   repeat
      y:=y+5;
      x:=x+5;
      delay(25);
      circle(x,y,10);
   until y>340;

   repeat
      x:=x-5;
      delay(25);
      circle(x,y,10);
   until x<40;

   repeat
      y:=y-5;
      delay(25);
      circle(x,y,10);
   until y<40;

  until keypressed;
  closegraph;
  end.