public int upgradeRoom(int room_number,String start_day,int period){
		String type_query = "select type from room where room_number="+room_number;
		String type = helper.executeSelectQuery(type_query)[0][0].toString();
//		System.out.println(type);
		String new_type="";
		//  standard / superior / deluxe / suite Դϴ. (ϼ  )
		if(type.equals("standard")){
			new_type = "superior";
		}else if(type.equals("superior")){
			new_type = "deluxe";
		}else if(type.equals("deluxe")){
			new_type = "suite";
		}else if(type.equals("suite")){
			return room_number;
		}
		
		String find_room_query = "select room_number from room where type='"+new_type+"'";
//		System.out.println(find_room_query);
		
		Object[][] room = helper.executeSelectQuery(find_room_query);
		
		
		for(int i=0;i<room.length;i++){
			for(int j=0;j<room[i].length;j++){
//				System.out.println(room[i][j].toString());
				if(!checkRoom(new Integer(room[i][j].toString()).intValue(), start_day,period)){
//					System.out.println(room[i][j].toString());
					return new Integer(room[i][j].toString()).intValue();
				}
			}
		}
		return room_number;
	}