private int currentPos = 0;
    private int maxPoses;
    private int minPoses;

void Update(){
        if (Input.GetKeyDown(KeyCode.D) || Input.GetKeyDown(KeyCode.RightArrow))
        {
            Move(1);
        }
        else(Input.GetKeyDown(KeyCode.A) || Input.GetKeyDown(KeyCode.LeftArrow))
        {
            Move(-1);
        }
}

    private void Move(int dir)
    {
        if (dir > 0)
        {
            if (currentPos < maxPoses)
            {
                transform.position += Vector3.right;
                currentPos += 1;
            }
        }
        else
        {
            if (currentPos > minPoses)
            {
                transform.position += Vector3.left;
                currentPos -= 1;
            }
        }
    }