#include <bits/stdc++.h>
using namespace std;
#define LL long long
#define MP(a, b) make_pair(a, b)
const int MAXN = 1000 + 10;
const int INF = 0x3f3f3f3f;
 
queue<int> qu;
priority_queue<int> pqu;
stack<int> stk;
 
struct COM
{
    int a, num;
}cmd[MAXN];
 
int vis[4];
 
void Init()
{
    while (!qu.empty())
        qu.pop();
    while (!pqu.empty())
        pqu.pop();
    while (!stk.empty())
        stk.pop();
}
 
int main()
{
    //freopen("input.txt", "r", stdin);
    int n, i, j;
    while (~scanf("%d", &n))
    {
        int ans = 0;
        memset(vis, 0, sizeof vis);
        Init();
        for (i = 0; i < n; i++)
            scanf("%d%d", &cmd[i].a, &cmd[i].num);
        for (i = 0; i < n; i++)
        {
            if (cmd[i].a == 1)
                qu.push(cmd[i].num);
            else if (cmd[i].a == 2)
                if (qu.empty() || qu.front() != cmd[i].num)
                    break;
                else
                    qu.pop();
        }
        if (i == n)
            vis[1] = 1, ans++;
        for (i = 0; i < n; i++)
        {
            if (cmd[i].a == 1)
                stk.push(cmd[i].num);
            else if (cmd[i].a == 2)
                if (stk.empty() || stk.top() != cmd[i].num)
                    break;
                else
                    stk.pop();
        }
        if (i == n)
            vis[2] = 1, ans++;
        for (i = 0; i < n; i++)
        {
            if (cmd[i].a == 1)
                pqu.push(cmd[i].num);
            else if (cmd[i].a == 2)
                if (pqu.empty() || pqu.top() != cmd[i].num)
                    break;
                else
                    pqu.pop();
        }
        if (i == n)
            vis[3] = 1, ans++;
        if (ans == 0)
            printf("impossible\n");
        else if (ans > 1)
            printf("not sure\n");
        else
        {
            if (vis[1])
                printf("queue\n");
            else if (vis[2])
                printf("stack\n");
            else
                printf("priority queue\n");
        }
    }
    return 0;
}