function setup() {
  createCanvas(400, 400);

  var small_square_length = 40;
  var x_gap = (400 - small_square_length * 8) / 9;
  var y_gap = (400 - small_square_length * 8) / 9;

  background(220);

  var k = 0;
  for (var i = 0; i < 8; i++) {
    for (var j = 0; j < 8; j++) {
      if (k % 5 == 0) {
        const c = color(255, 0, 0);
        fill(c);
      } else {
        const c = color(255, 255, 255);
        fill(c);
      }

      rect(
        x_gap + small_square_length * j + x_gap * j,
        y_gap + small_square_length * i + y_gap * i,
        small_square_length,
        small_square_length,
      );

      if (k % 5 == 0) {
        const c = color(255, 255, 255);
        fill(c);
      } else {
        const c = color(0, 0, 0);
        fill(c);
      }
      textSize(16);
      textAlign(CENTER, CENTER);
      text(
        k,
        x_gap * (j + 1) + small_square_length * j + small_square_length / 2,
        y_gap * (i + 1) + small_square_length * i + small_square_length / 2,
      );

      k += 1;
    }
  }
}

function draw() {}