#include<iostream>
#include<string>
using namespace std;

const int N = 1E5+10;
int qu[N],hh=0,tt=-1;// 设置头指针和尾指针

int main(){
    int m;
    cin>>m;
    while(m--){
        string str;
        cin>>str;
        if(str == "push"){
            int x;
            cin>>x;
            qu[++tt] = x;
        }
        else if(str == "pop")
            hh++;
        else if(str == "empty"){
            if(hh<=tt)//tt初始设为-1
                cout<<"NO"<<endl;
            else cout<<"YES"<<endl;
        }
        else cout<<qu[hh]<<endl;
    }
    return 0;
}