def calculate_net_profit_loss(events):
    stocks = {}
    transactions = []
    result = []

    for event in events:
        event_parts = event.split()
        if event_parts[0] == 'BUY':
            stock_name = event_parts[1]
            quantity = int(event_parts[2])
            if stock_name not in stocks:
                stocks[stock_name] = {'quantity': quantity, 'price': 0}
            else:
                stocks[stock_name]['quantity'] += quantity
        elif event_parts[0] == 'SELL':
            stock_name = event_parts[1]
            quantity = int(event_parts[2])
            if stock_name in stocks and stocks[stock_name]['quantity'] >= quantity:
                stocks[stock_name]['quantity'] -= quantity
            else:
                return "Invalid sell operation"
        elif event_parts[0] == 'CHANGE':
            stock_name = event_parts[1]
            price_change = float(event_parts[2])
            if stock_name in stocks:
                stocks[stock_name]['price'] += price_change
            else:
                return "Invalid stock price change operation"
        elif event_parts[0] == 'QUERY':
            net_profit_loss = sum(
                stocks[stock]['quantity'] * stocks[stock]['price'] for stock in stocks
            )
            result.append(net_profit_loss)

    return result


events = [
    "BUY stock2 2", "BUY stock1 4", "CHANGE stock2 -8", "SELL stock1 2", "BUY stock3 3", "QUERY"
]

print(calculate_net_profit_loss(events))