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(a1){
int b;
cin>>b;
s.push(b);
}
else if(a2){
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;
}