Queue

Implement a queue that stores integers, then process the commands given in the input in order.

There are six commands.

• push X: put the integer $X$ into the queue.
• pop: remove the integer at the front of the queue and print it. Print -1 if the queue is empty.
• size: print how many integers the queue holds.
• empty: print 1 if the queue is empty and 0 otherwise.
• front: print the integer at the front of the queue. Print -1 if the queue is empty.
• back: print the integer at the back of the queue. Print -1 if the queue is empty.

The first line contains the number of commands $N$ ($1 \le N \le 10\,000$).

Each of the next $N$ lines contains one command. Every integer given with push is at least $1$ and at most $100\,000$. No command outside the list above appears.

For each command that prints something, print its result on its own line. If no command prints anything, print nothing.