arq-maratona

#include <bits/stdc++.h>

using namespace std;

#define STK 1
#define PQ 2
#define QUEUE 3


int x, pos_in, pos_out, n, in[ 10050 ], out[ 10050 ];

bool test_queue();
bool test_stack();
bool test_priority();

int main(){

	while( cin >> n ){
		pos_in = pos_out = 0;

		for(int cases = 0; cases < n; cases++){
			cin >> x;

			if(x == 1) cin >>  in[ pos_in++ ];
			else       cin >> out[ pos_out++ ];
		}

		int a = 0, b = 0, c = 0;

		if( test_queue()    ) b = QUEUE;
		if( test_stack()    ) c = STK;
		if( test_priority() ) a = PQ;

		if(pos_in == 1 || pos_out == 1)
			a = b = c = 1;

		if(a && b && c)
			cout << "impossible" << endl;
		else if( (a&&b) || (b&&c) || (a&&c) )
			cout << "not sure" << endl;

		else if(a) cout << "priority queue" << endl;
		else if(b) cout << "queue" << endl;
		else if(c) cout << "stack" << endl;
	}

	return 0;

}

bool test_stack(){
	for(int i = 0; i < pos_out; i++)
		if(in[i] != out[ pos_in-i-1 ] )
			return false;

	return true;
}

bool test_queue(){
	for(int i = 0; i < pos_out; i++)
		if( in[i] != out[i] )
			return false;

	return true;
}

bool test_priority(){
	for(int i = 1; i < pos_out; i++)
		if( out[i] > out[i-1])
			return false;

	return true;
}