关于m个苹果每天吃一个或者两个，有几种吃法

function sliceNum($num){
    if($num == 1){
        return $num;
    }elseif ($num == 2){
        return $num;
    }else{
       return  $this->sliceNum($num-1)+$this->sliceNum($num-2);
    }
}