void Update () {
        if (Input.GetKeyDown(KeyCode.A))
            {Vector3 position = this.transform.position;
            position.x--;
            this.transform.position = position;

        }
        if (Input.GetKeyDown(KeyCode.D))
        {
            Vector3 position = this.transform.position;
            position.x--;
            this.transform.position = position;

        }
        if (Input.GetKeyDown(KeyCode.W))
        {
            Vector3 position = this.transform.position;
            position.y++;
            this.transform.position = position;

        }
        if (Input.GetKeyDown(KeyCode.S))
        {
            Vector3 position = this.transform.position;
            position.y++;
            this.transform.position = position;

        }
    }