Queue using Two Stacks

You are required to implement a queue using two stacks. The queue should support four operations:

• enqueue x: Insert an integer x at the end of the queue.
• dequeue: Remove and return the element at the front of the queue. If the queue is empty, return -1.
• peek: Return the element at the front of the queue without removing it. If the queue is empty, return -1.
• isEmpty: Return whether the queue is empty. Output True if it is empty and False otherwise.

Implement the above operations using two stacks so that the overall behavior is that of a FIFO (first-in-first-out) queue.

All operations that produce an output (i.e. dequeue, peek, and isEmpty) should have their results printed in the order of execution, each on a new line.

inputFormat

The first line of input contains a single integer n (1 ≤ n ≤ 10⁵), which is the number of operations to be performed on the queue.

Each of the following n lines contains one of the following commands:

• enqueue x where x is an integer.
• dequeue
• peek
• isEmpty

Note: The enqueue command does not produce any output.

outputFormat

For each command that produces an output (dequeue, peek, isEmpty), print the result on a new line in the order the commands are executed.

For dequeue and peek, if the queue is empty, output -1.
For isEmpty, output True if the queue is empty, otherwise output False.

## sample

7
enqueue 10
enqueue 20
peek
dequeue
npeek
dequeue
dequeue

10
10
20
-1

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