Stack Book Organizer

Raj has a stack of books he wants to organize. Each book is identified by a unique positive integer. He can perform three types of operations:

• Add: Push a book onto the top of the stack.
• Remove: Remove the book from the top of the stack (if the stack is not empty).
• Check: Check whether a book with a given ID is currently present in the stack. If it is, output "YES"; otherwise, output "NO".

You are given a series of operations. For each check operation, output the corresponding result. The operations are processed in the order given.

Note: The operations are described by a string and an integer. The integer represents the book ID. The operations are defined as follows:

\( \text{add:} \quad \text{Push the book onto the stack.} \)

\( \text{remove:} \quad \text{If the stack is non-empty, remove the top book.} \)

\( \text{check:} \quad \text{Output \( YES \) if the book is in the stack; otherwise, output \( NO \).} \)

inputFormat

The input is given via standard input. The first line contains a single integer \( n \) which denotes the number of operations. The next \( n \) lines each contain an operation in the format:

<operation> <book_id>

Where <operation> is one of "add", "remove", or "check" and <book_id> is a positive integer.

outputFormat

For every operation of type check, output a single line containing either "YES" or "NO" depending on whether the book with the given ID is in the stack at that moment.

## sample

5
add 5
add 3
check 5
remove 3
check 3

YES
NO

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