public int getAliveNum(){
		int tankAlive = 0 ; 
		
		for(Enemy e : this.enemyList){
			if( e.getStatus() == Tank.ALIVE || e.getStatus() == Tank.SLEEP)
				tankAlive ++ ;
		}
		
		this.totleKilledThisStage = this.enemyList.size() - tankAlive ;
		return tankAlive ;
	}