#include <iostream>
using namespace std;
const int N=1e5+10;
int stk[N],tt,m;
int main()
{
cin>>m;
while(m--)
{
int x;
string op;
cin>>op;
if(op=="push")
{
cin>>x;
stk[++tt]=x;
}
else if(op=="pop") tt--;
else if(op=="empty") cout<<(tt ? "NO" : "YES" )<<endl;
else cout << stk[tt] <<endl;
}
return 0;
}