eval(s=(%w@
  q=$*[0]&.to_i;

  z="eval(s=(%w#{64.chr}#{s}##{s*9}#{64.chr}.join))";

  h=25;w=80;
  px=2;py=h/2;
  vx=0.5;vy=-0.5;
  qx=w-3;qy=h/2;
  ux=-0.5;uy=0.5;

  b=Array.new(h*w){|i|
    y=i/w;
    x=i%w;
    (x==0||x==w-1||y==0||y==h-1)?2:(w/2<x)?1:0
  };

  f=->(x,y,vx,vy,c){
    sx=vx;sy=vy;
    8.times{|i|
      t=i*Math::PI/4;
      cos=Math.cos(t);
      sin=Math.sin(t);
      nx=x+cos/2;
      ny=y+sin/2;
      k=ny.to_i*w+nx.to_i;
      if(0<=nx&&nx<w&&0<=ny&&ny<h&&b[k]!=c);
        b[k]==2?0:b[k]=c;
        (sin.abs<cos.abs)?sx*=-1:sy*=-1;
      end
    };
    [sx,sy]
  };
  g=->(x,y,vx,vy){
    [(x+vx<0||w<=x+vx)?-vx:vx,(y+vy<0||h<=y+vy)?-vy:vy]
  };

  j=0;
  loop{
    j+=1;
    (vx,vy=f[px,py,vx,vy,0]);
    (vx,vy=g[px,py,vx,vy]);
    px+=vx;
    py+=vy;
    (ux,uy=f[qx,qy,ux,uy,1]);
    (ux,uy=g[qx,qy,ux,uy]);
    qx+=ux;
    qy+=uy;
    q&&((q<j)?(break):(q!=j)?(next):0);
    q||(print"\e[H\e[2J");
    c=[];
    h.times{|y|
      w.times{|x|
        c<<!(b[y*w+x]==0&&[px.to_i,py.to_i]!=[x,y]||[qx.to_i,qy.to_i]==[x,y])
      };
    };
    t=c.count(!!0);
    i=0;
    h.times{|y|
      w.times{|x|
        print((y==h-1&&x>=w-8)?"#{64.chr}.join))"[8+x-w]:c[y*w+x]?[z[i],i+=1][0]:32.chr)
      };
      puts;
    };
    sleep(0.05);
  }

@.join))