const N = 70; // min=10, max=100, step=1
const ROT = 7.; // min=0, max=100, step=1
const SIZE = 5; // min=1, max=100, step=1

Canvas.setpenopacity(0.8);
const turtle = new Turtle();

function box(size) {
    turtle.penup();
    turtle.forward(-size/2);
    turtle.right(90);
    turtle.forward(-size/2);
    turtle.left(90)
    turtle.pendown();

    for (j = 0; j < 4; j++) {
        turtle.forward(size);
        turtle.right(90);
    }
}

function walk(i) {
    size = SIZE * i;
    turtle.penup();
    turtle.goto(0, 0);
    turtle.pendown();
    turtle.right(i/ROT)
    box(size)
    return i < N;
}