size(300,300);

for(int i=0; i<300 ; i=i+40){

  for(int t=0; t<300 ; t=t+40){

    fill(0,0,0);
    rect(t,i,40,40);


    fill(255,255,255);

    rect(30+t,30+i,10,10);
    rect(t,i,10,10);

  }
}

rect(0,0,40,40);
rect(0,80,40,40);
rect(0,240,40,40);
rect(0,160,40,40);
rect(40,200,40,40);
rect(40,280,40,40);
rect(40,120,40,40);
rect(40,40,40,40);
rect(80,0,40,40);
rect(80,80,40,40);
rect(80,160,40,40);
rect(80,240,40,40);
rect(120,40,40,40);
rect(160,0,40,40);
rect(160,80,40,40);
rect(120,120,40,40);
rect(120,200,40,40);
rect(160,160,40,40);
rect(160,240,40,40);
rect(200,280,40,40);
rect(200,200,40,40);
rect(200,120,40,40);
rect(200,40,40,40);
rect(240,0,40,40);
rect(240,80,40,40);
rect(240,160,40,40);
rect(240,240,40,40);
rect(280,40,40,40);
rect(280,120,40,40);
rect(280,200,40,40);
rect(280,280,40,40);
rect(120,280,40,40);