#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;
}