private void OnTriggerStay2D(Collider2D other)
 {
     if (other.gameObject.tag == "Monster")
     {
         if (Time.time - lastAttackTime > coolTime)
         {
             int damage = character.GetComponent <CharacterStat>().damage;
             characterBehavior.attack(damage);
             lastAttackTime = Time.time;
         }
     }
 }