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

queue<int> q;
void solve(){
	int choose;cin>>choose;
	if(choose == 1){
		int a;cin>>a;
		q.push(a);
	}else if(choose == 2){
		if(q.empty()){
			cout << "ERR_CANNOT_POP" << endl;
		}else{
			q.pop();
		}
	}else if(choose == 3){
		if(q.size()){
			cout << q.front() << endl;
		}else{
			cout << "ERR_CANNOT_POP" << endl;
		} 
	}else if(choose == 4){
		cout << q.size() << endl;
	}
}

signed main() {
    ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    int n;cin>>n;
    
    while(n--){
    	solve();
	}
    return 0;
}