def clear():
    for r in range(rows):
        for c in range(rows):
            if r%3 == 1 and c%3 == 1:
                color = brown;
                grid[r][c] = 1;
            else:
                color = white;
                grid[r][c] = 0;
            pygame.draw.rect(screen, color, [(margin+width)*c+margin, (margin+height)*r+margin, width, height])
    pygame.display.flip();