1 /*by SilverN*/ 2 #include<algorithm> 3 #include<iostream> 4 #include<cstring> 5 #include<cstdio> 6 #include<cmath> 7 #include<vector> 8 #include<queue> 9 #include<stack>10 using namespace std;11 int read(){12     int x=0,f=1;char ch=getchar();13     while(ch<‘0‘ || ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}14     while(ch>=‘0‘ && ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}15     return x*f;16 }17 priority_queue<int>q;18 stack<int>st;19 queue<int>que;20 int n;21 int x,y;22 bool flag_st,flag_qu,flag_pr;23 int main(){24 /*    freopen("qu.in","r",stdin);25     freopen("qu.out","w",stdout);*/26     27     while(scanf("%d",&n)!=EOF){28         int i,j;29         flag_pr=flag_qu=flag_st=1;30         while(!q.empty()) q.pop();31         while(!st.empty()) st.pop();32         while(!que.empty()) que.pop();33         for(i=1;i<=n;i++){34             scanf("%d%d",&x,&y);35             if(x==1){36                 q.push(y);37                 st.push(y);38                 que.push(y);39             }40             else{41                 if(q.empty() || q.top()!=y)flag_pr=0;42                 if(st.empty() || st.top()!=y)flag_st=0;43                 if(que.empty() || que.front()!=y)flag_qu=0;44                 if(!q.empty())q.pop();45                 if(!st.empty()) st.pop();46                 if(!que.empty()) que.pop();47             }48         }49         int cnt=0;50         if(flag_st)cnt++; if(flag_pr)cnt++; if(flag_qu)cnt++;51         if(cnt>1){52             printf("not sure\n");53             continue;54         }55         if(flag_st && !flag_pr && !flag_qu)printf("stack\n");56         if(!flag_st && !flag_pr && flag_qu)printf("queue\n");57         if(!flag_st && flag_pr && !flag_qu)printf("priority queue\n");58         if(!flag_st && !flag_pr && !flag_qu)printf("impossible\n");59     }60     return 0;61 }