求掉

#include<iostream>
#include<list>
using namespace std;
int n;
list<int> a[1000050];
int main(){
	cin>>n;
	while(n--){
		int x,y;
		string s;
		cin>>s;
		if(s=="push_back"){
			cin>>x>>y;
			a[x].push_back(y);
		}
		else
			if(s=="pop_back"){
				cin>>x;
				if(!a[x].empty())
					a[x].pop_back();
			}
			else
				if(s=="size"){
					cin>>x;
					cout<<a[x].size();
				}
				else
					if(s=="push_front"){
						cin>>x>>y;
						a[x].push_front(y);
					}
					else
						if(s=="pop_front"){
							cin>>x;
							if(!a[x].empty())
								a[x].pop_front();
						}
						else
							if(s=="front"){
								cin>>x;
								if(!a[x].empty())
									cout<<a[x].front()<<'\n';
							}
							else
								if(s=="back"){
									cin>>x;
									if(!a[x].empty())
										cout<<a[x].back()<<'\n';
								}
	}
	return 0;
}