#include <bits/stdc++.h>
using namespace std;

int main() {
	queue <int> q;
	int n,a,ans=0;
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a;
		if(a==1){
			cin>>ans;
			q.push(ans);
		}else if(a==2){
			if(q.size()==0){
				cout<<"ERR_CANNOT_POP"<<"\n";
			}
			q.pop();
		}else if(a==3){
			if(q.size()==0){
				cout<<"ERR_CANNOT_QUERY"<<"\n";
			}
			cout<<q.front()<<"\n";
		}else if(a==4){
			cout<<q.size();
		}
	}
	return 0;
}

救救孩子吧，要改崩溃了。