#include <bits/stdc++.h>
using namespace std;
const unsigned long long N = 100010;
long long m;
long long a[N], t;
int main()
{
	scanf("%d", &m);
	while (m-- )
	{
		string op;
		unsigned long long x;
		cin >> op;
		if (op == "push")
		{
			scanf("%d", &x);
			a[ ++ t] = x;
		}
		else if (op == "pop") t--;
		else if (op == "empty")
		{
			if (t > 0) printf("NO\n");
			else printf("YES\n");
		}
		else
		{
			printf("%d\n", a[t]);
		}
	}
	return 0;
}