模板：堆

https://www.luogu.org/problemnew/show/P3378

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<queue>
using namespace std; 
priority_queue<int,vector<int>,greater<int> >q;
int main(){
     int n;
     scanf("%d",&n);
     for(int i=1; i<=n; i++){
          int x;
          scanf("%d",&x);
          if(x==1){
              scanf("%d",&x);
            q.push(x);
        }
      else if(x==2) printf("%d\n",q.top());
      else     q.pop();       
     } 
    return 0;  
}