题解

#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin>>n;
    queue<int> s;
    for(int i = 1;i <= n;i++){
        int a;
        cin>>a;
        if(a==1){
            int b;
            cin>>b;
            s.push(b);
        }
        else if(a==2){
            if(!s.empty()){
                s.pop();
            }else{
                cout<<"impossible!"<<endl;
            }
        }
        else if(a==3){
            if(!s.empty()){
                cout<<s.front()<<endl;
            }else cout<<"impossible!"<<endl;
        }
    }
    return 0;
}