Library Book Management System

You are required to implement a simple library management system which supports three operations:

• BORROW: A user borrows a book. If the book is available (i.e. its stock is greater than 0), it will decrease the stock by 1 and return SUCCESS; otherwise, it returns OUT OF STOCK.
• RETURN: A user returns a book. This operation increases the stock by 1 for the book and returns RETURNED.
• STOCK: Check the available stock for a given book, printing the current stock as an integer.

Internally, the system starts with zero stock for every book. A book's stock is only increased when a RETURN command is executed. You may assume that any RETURN command is valid. The operations follow the rules below:

For a book with ID B, let its current stock be \( S_B \). Then:

• For BORROW: If \( S_B > 0 \) then update \( S_B \gets S_B - 1 \) and print SUCCESS; otherwise, print OUT OF STOCK.
• For RETURN: Update \( S_B \gets S_B + 1 \) and print RETURNED.
• For STOCK: Output the integer value \( S_B \).

inputFormat

The input is read from standard input and consists of multiple lines. The first line contains a single integer \( N \) representing the number of commands. Each of the following \( N \) lines contains one command. Each command is one of the following formats:

• STOCK <book_id>
• BORROW <user_id> <book_id>
• RETURN <user_id> <book_id>

outputFormat

The output should be printed to standard output. For each command, output the result on a new line. The possible outputs are:

• An integer (for the STOCK command).
• The strings SUCCESS, OUT OF STOCK, or RETURNED for BORROW and RETURN commands.

## sample

6
STOCK B001
BORROW U001 B001
STOCK B001
BORROW U002 B001
RETURN U001 B001
STOCK B001

0
OUT OF STOCK
0
OUT OF STOCK
RETURNED
1

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