题解

#include<iostream>
#include<queue>
using namespace std;
int main(){
    int n;
	queue<int>q;
	cin>>n;
	for(int i=0;i<n;i++){
        int x;
		cin>>x;
		if(x==1){
            int p;
			cin>>p;
			q.push(p);
		}else if(x==2){
			if(q.empty()!=0){
				cout<<"impossible!\n";
			}else{
				q.pop();
			}
		}else{
			if(q.empty()!=0){
				cout<<"impossible!\n";
			}else{
				cout<<q.front()<<'\n';
			}
		}
	}
	return 0;
}