#include <bits/stdc++.h> using namespace std; int main() { int m; cin >> m; stack<int> q; while (m--) { string op; cin >> op; if (op == "push") { int x; cin >> x; q.push(x); } if (op == "pop") q.pop(); if (op == "empty") cout << (q.empty() ? "YES" : "NO") << endl; if (op == "query") cout << q.top() << endl; } return 0; }