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

const int N = 100010;
int st[N];
int top = -1;
int n, x;

void push(int x) {
    st[ ++ top] = x;
}

void pop() {
    top -- ;
}

string empty() {
    if (top == -1) return "YES";
    else return "NO";
}

int query() {
    return st[top];
}


int main() {
    cin >> n;
    while (n -- ) {
        string opt;
        cin >> opt;
        if (opt == "push") {
            cin >> x;
            push(x);
        }
        if (opt == "pop") pop();
        if (opt == "empty") cout << empty() << endl;
        if (opt == "query") cout << query() << endl;
    }

}