uses graph;
const grtegur=800.0;
 procedure joonista_post(x, y, z: integer);
 begin
  rectangle(300+round(x*grtegur/z), 250-round(y*grtegur/z),
            300+round((x+10)*grtegur/z), 250-round((y-100)*grtegur/z));
 end;

var d, m, kaugus: integer;
begin
 d:=detect; initgraph(d, m, '');
 kaugus:=1000;
 setcolor(white);
 while(kaugus<3000)do
 begin
       joonista_post(-300, -100, kaugus);
       joonista_post( 100, -100, kaugus);
       kaugus:=kaugus+100;
 end;
 readln; closegraph;
end.