#include<bits/stdc++.h>
#include <queue>
using namespace std;
queue<int> s1;
int main ()
{
	int n,m,x,y;
	cin>>n;
	int a[m];
	for(int i=1;i<=n;i++)
	{
		cin>>a[i];
		if(a[i]==1)
		{		cin>>x;
		s1.push(x);
		}
		if(a[i]==2)
		{
			if(s1.empty()==0)
			s1.pop();
			else
			cout<<"ERR_CANNOT_POP";
		}
		if(a[i]==3&&s1.size()>0)
		{
			cout<<s1.front();
		}
		if(a[i]==3&&s1.size()==0)
		{
			cout<<"ERR_CANNOT_QUERY";
		}
		if(a[i]==4)
		cout<<s1.size();
	}
	return 0;
}