P1036

#include<bits/stdc++.h>
using namespace std;
int n, l, r, m,ans; 
int a[1000], w[10000],b[100000],c[100000];
queue<int>q;
int main() {
    cin >>n;
    for(int i = 1; i <= n; i++){
		cin>>m;
		if(m ==1){
			cin>>m;
			q.push(m);
		} 
		if(m ==2){
			if(q.empty())
				cout<<"ERR_CANNOT_POP";
			else q.pop();
		}
		if(m ==3){
			if(q.empty())
				cout<<"ERR_CANNOT_POP";
			else q.front();
		} 
		if(m ==4){
			q.size();
		}
	}
}