UVA

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<string>
#include<cmath>
#include<map>
#include<set>
#include<vector>
#include<queue>
#include<bitset>
#include<ctime>
#include<deque>
#include<stack>
#include<functional>
#include<sstream>
//#include<cctype>
//#pragma GCC optimize(2)
using namespace std;
#define maxn 100005
#define inf 0x7fffffff
//#define INF 1e18
#define rdint(x) scanf("%d",&x)
#define rdllt(x) scanf("%lld",&x)
#define rdult(x) scanf("%lu",&x)
#define rdlf(x) scanf("%lf",&x)
#define rdstr(x) scanf("%s",x)
#define mclr(x,a) memset((x),a,sizeof(x))
typedef long long  ll;
typedef unsigned long long ull;
typedef unsigned int U;
#define ms(x) memset((x),0,sizeof(x))
const long long int mod = 1e9;
#define Mod 1000000000
#define sq(x) (x)*(x)
#define eps 1e-5
typedef pair<int, int> pii;
#define pi acos(-1.0)
//const int N = 1005;
#define REP(i,n) for(int i=0;i<(n);i++)
typedef pair<int, int> pii;

inline int rd() {
	int x = 0;
	char c = getchar();
	bool f = false;
	while (!isdigit(c)) {
		if (c == '-') f = true;
		c = getchar();
	}
	while (isdigit(c)) {
		x = (x << 1) + (x << 3) + (c ^ 48);
		c = getchar();
	}
	return f ? -x : x;
}


ll gcd(ll a, ll b) {
	return b == 0 ? a : gcd(b, a%b);
}
int sqr(int x) { return x * x; }



/*ll ans;
ll exgcd(ll a, ll b, ll &x, ll &y) {
	if (!b) {
		x = 1; y = 0; return a;
	}
	ans = exgcd(b, a%b, x, y);
	ll t = x; x = y; y = t - a / b * y;
	return ans;
}
*/
int n;


int main()
{
//	ios::sync_with_stdio(0);
	while (cin >> n) {
		stack<int>sk;
		queue<int>qu;
		priority_queue<int>q;
		bool fg1 = 1, fg2 = 1, fg3 = 1;
		for (int i = 1; i <= n; i++) {
			int opt; opt = rd();
			if (opt == 1) {
				int x = rd();
				if (fg1)sk.push(x);
				if (fg2)qu.push(x);
				if (fg3)q.push(x);
			}
			else {
				int x = rd();
				if (!sk.empty() && sk.top() == x && fg1)sk.pop();
				else fg1 = 0;
				if (!qu.empty() && qu.front() == x && fg2)qu.pop();
				else fg2 = 0;
				if (!q.empty() && q.top() == x && fg3)q.pop();
				else fg3 = 0;
			}
		}
		int ans = fg1 + fg2 + fg3;
		if (!ans)cout << "impossible" << endl;
		else {
			if (ans == 1) {
				if (fg1 == 1)cout << "stack" << endl;
				else if (fg2)cout << "queue" << endl;
				else if (fg3)cout << "priority queue" << endl;
			}
			else cout << "not sure" << endl;
		}
	}
	return 0;
}