#include<bits/stdc++.h>
using namespace std;
const int N = 100010;
int stk[N],top;
int m;
int main(){
    cin >> m;
    while(m--){
        int x;
        string st;
        cin >> st;
        if(st == "push"){
            cin >> x;
            stk[++top] = x;
        }else if(st == "query"){
            cout << stk[top] << endl;
        }else if(st == "pop"){
            --top;
        }else{
            if(top == 0){
                cout << "Yes" << endl;
            }else{
                cout << "No" << endl;
            }
        }
    }
    // while(top){
    //     cout << stk[top] << endl;
    //     top--;
    // }
    return 0;
}