uses
  graph;

const
  r1=100;
  r2=200;
var
  dr,lo,hi,x,y,i,step:integer;
  r3,r4:real;

begin
  dr:=detect;
  getmoderange(dr,lo,hi);
  initgraph(dr,hi,'e:\bp\bgi');
  SetBkColor(8);
  setcolor(12);
  circle(getmaxx div 2, getmaxy div 2,r1);
  line(670,370,670,770);
  line(690,370,690,770);
  line(670,370,690,370);
  circle(getmaxx div 2, getmaxy div 2,r2);
  i:=0;
  r3:=r1+(r2-r1)/2;
  r4:=(r2-r1)/2;
  step:=round(2*(180-360*arctan(2*sqrt(sqr(r3)-sqr(r4/2))/(r4))/pi));
  while (360 mod step <> 0) do inc(step);
  setcolor(10);
  while i<=360 do begin
    x:=round(r3*cos(i*pi/180)) + getmaxx div 2;
    y:=round(r3*sin(i*pi/180)) + getmaxy div 2;
    circle(x,y,round(r4));
    inc(i,step);
  end;
  readln;
  closegraph;
end.