听说灌水区dalao多我就来求助了

该题目链接：here

一道队列模板题，可惜我这个只会vector和普通数组的蒟蒻做不出来 代码：

#include<bits/stdc++.h>
using namespace std;
typedef unsigned long long ll;
queue<ll>A;
signed main(){
    ll F;
    scanf("%llu",&F);
    while(F--){
        ll pd;
        scanf("%llu",&pd);
        if(pd==1){
            ll X;
            scanf("%llu",&X);
            A.push(X);
        }
        else if(pd==2){
            if(A.empty()){
            	printf("ERR_CANNOT_POP\n");
            }
            else A.pop();
        }
        else if(pd==3){
            if(A.empty()){
                printf("ERR_CANNOT_POP\n");
            }
            else printf("%llu\n",A.front());
        }
        else{printf("%llu\n",A.size());}
    }
    return 0;
}

(我很菜别喷