Program  Sample;
 uses  graph, crt;

 const 
	RADIUS =  20 ;
   DELTA =  10 ;

 var  gd, gm:integer;

	oldRelative: integer;
   centerX: integer;
   position: integer;

 procedure  drawCircles(relative:integer);
 begin 

   setColor(black);

 	circle(oldRelative + RADIUS, GetMaxY  div   2 , RADIUS);
  	circle(GetMaxX - (oldRelative + RADIUS), GetMaxY  div   2 , RADIUS);

   setColor(white);
	 if  (relative + RADIUS + DELTA > centerX)  then   begin 
    	setColor(green);
     	circle(GetMaxX  div   2 , GetMaxY  div   2 , RADIUS);
    end   else   begin 
	   circle(relative + RADIUS, GetMaxY  div   2 , RADIUS);
   	circle(GetMaxX - (relative + RADIUS), GetMaxY  div   2 , RADIUS);
    end ;
   oldRelative := relative;


 end ;

 begin 

	gd:=vga;
	gm:=vgahi;
	initgraph(gd,gm,'');

   oldRelative :=  0 ;
   position :=  0 ;

   centerX := GetMaxX  div   2 ;

   setColor(white);

	 while  position + RADIUS < centerX  do   begin 
		drawCircles(position);
      inc(position, DELTA);
      readkey;
    end ;


   closegraph;
 end .