class program {

define half-turn() {
    turnleft();
    turnleft();
}

define go-back() {
    half-turn();
    if (frontIsClear) {
        move();
    }
    half-turn();
}

define tile(odd) {
    if (notNextToABeeper) {
        if (! iszero(odd)) {
            putbeeper();
        }
        iterate (4) {
            if (frontIsClear) {
                move();
                if (iszero(odd)) {
                    tile(1);
                } else {
                    tile(0);
                }
            }
            turnleft();
        }
    }
    go-back();
}

program() {
    tile(1);
    turnoff();
}

}