beecrowd | 1340
# I Can Guess the Data Structure!

**Timelimit: 2**

By Rujia Liu China

There is a bag-like data structure, supporting two operations:

1 x

Throw an element x into the bag.

2

Take out an element from the bag.

Given a sequence of operations with return values, you're going to guess the data structure. It is a stack (Last-In, First-Out), a queue (First-In, First-Out), a priority-queue (Always take out larger elements first) or something else that you can hardly imagine!

There are several test cases. Each test case begins with a line containing a single integer **n** (1 <= **n** <= 1000). Each of the next **n** lines is either a type-1 command, or an integer 2 followed by an integer **x**. That means after executing a type-2 command, we get an element **x** *without error*. The value of **x** is always a positive integer not larger than 100. The input is terminated by end-of-file (EOF). The size of input file does not exceed 1MB.

For each test case, output one of the following:

stack

It's definitely a stack.

queue

It's definitely a queue.

priority queue

It's definitely a priority queue.

impossible

It can't be a stack, a queue or a priority queue.

not sure

It can be more than one of the three data structures mentioned above.

Sample Input | Sample Output |

6 |
queue |