Implementing a Custom Queue with Basic Operations

You are required to implement a queue data structure supporting the following operations:

• push(x): Insert a number \(x\) into the queue.
• pop(): Remove the front element from the queue. If the queue is empty, do not remove any element and output ERR_CANNOT_POP.
• query(): Output the front element of the queue. If the queue is empty, output ERR_CANNOT_QUERY.
• size(): Output the current number of elements in the queue.

The commands will be provided in the input. The first line of the input contains an integer representing the number of operations. Each of the following lines contains one of the above commands. Note that the operations push do not produce any output, while pop, query, and size may result in printed output (if applicable).

inputFormat

The input consists of multiple lines.

1. The first line contains an integer \(n\) representing the number of operations.
2. The next \(n\) lines each contain a command, which can be one of the following:
• push x where \(x\) is an integer.
• pop
• query
• size

outputFormat

For each command that produces an output (pop when the queue is empty, query, and size), output the corresponding result on a new line.

If a pop command is executed on an empty queue, output ERR_CANNOT_POP.
If a query command is executed on an empty queue, output ERR_CANNOT_QUERY.

sample

5
push 10
push 20
query
pop
query

10
20