#include <iostream>
using namespace std;
const int N = 100010;
int stack[N], top, m;
string mode;

void init() {
    top = 0;
}

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

void pop() {
    top--;
}

int size() {
    return top;
}

int main() {
    cin >> m;
    init();
    while(m--) {
        int x;
        cin >> mode;
        if(mode == "push") cin >> x, push(x);
        if(mode == "pop") pop();
        if(mode == "empty") cout << (size() == 0 ? "YES\n" : "NO\n");
        if(mode == "query") cout << stack[top] << endl;
    }
}