#include <iostream>
#include <cstdio>
using namespace std;
const int N = 1E5 + 10;
int qu[N];
int hh, tt;
int main(){
    int n;  scanf("%d", &n);
    while(n -- ){
        string s;   cin >> s;
        if(s == "push"){
            int x;  scanf("%d", &x);
            qu[tt ++ ] = x;
        }else if(s == "query")  cout << qu[hh] << endl;
        else if(s == "pop") hh ++ ;
        else{
            if(hh >= tt) cout << "YES" << endl;
            else    cout << "NO" << endl;
        }
    }
    return 0;
}