public void Update()
 {
     if (times < 30 && flag == 0)
     {
         if (interval <= 0)
         {
             interval = Random.Range(3, 5);
             times++;
             int num = Random.Range(1, 4);
             for (int i = 0; i < num; i++)
             {
                 factory.produceUFO();
             }
         }
         interval -= Time.deltaTime;
     }
 }