private Vector3 point = Vector2.zero;
    private bool isMove = false;

    void Update()
    {
       if (Input.GetKey(KeyCode.UpArrow))
       {
           if (!isMove)
           {
               isMove = true;
               float step = (float) Math.Round(transform.position.z, 1) + 0.8f;

               if (transform.position.z + 0.8f == 0.0f)
               {
                   step = 0;
               }

               point = new Vector3(0, 0, step);
           }
       }
       else if (Input.GetKey(KeyCode.DownArrow))
       {
           if (!isMove)
           {
               isMove = true;
               float step = (float) Math.Round(transform.position.z, 1) - 0.8f;

               if (transform.position.z - 0.8f == 0.0f)
               {
                   step = 0;
               }

               point = new Vector3(0, 0, step);
           }
       }

       if (transform.position != point)
       {
           transform.position = Vector3.MoveTowards(transform.position, point, 2.0f * Time.deltaTime);
       }
       else
       {
           isMove = false;
       }
   }