#include<bits/stdc++.h>

using namespace std;

const int N = 100005;

int q[N], hh, tt = -1;

int main(){
    int m;
    cin>>m;
    while(m--){
        string op;
        int x;
        cin>>op;
        if(op == "push"){
            cin>>x;
            q[++tt] = x; 
        }
        else if(op == "pop"){
            hh++;
        }
        else if(op == "empty"){
            cout<<(tt >= hh ? "NO" : "YES")<<endl;
        }
        else if(op == "query"){
            cout<<q[hh]<<endl;
        }
    }
    return 0;
}