0分求调

#include<bits/stdc++.h>
using namespace std;
list<long long> v[1000010];
int a,q;
long long x;
string b;
inline int read()
{
    int k=0,f=1;
    char c=getchar();
    while(c<'0'||c>'9')
    {
        if(c=='-') f=-1;
        c=getchar();
    }
    while(c>='0'&&c<='9') k=(k<<1)+(k<<3)+(c^48),c=getchar();
    return k*f;
}
int main()
{
	q=read();
	for(int i=0;i<q;i++)
	{
		cin>>b;
		if(b=="pop_back")
		{
			a=read();
			if(v[a].empty()) continue;
			v[a].pop_back();
		}
		if(b=="pop_front")
		{
			a=read();
			if(v[a].empty()) continue;
			v[a].pop_front();
		}
		if(b=="push_back")
		{
			a=read(),x=read();
			v[a].push_back(x);
		}
		if(b=="push_front")
		{
			a=read(),x=read();
			v[a].push_front(x);
		}
		if(b=="back")
		{
			a=read();
			if(v[a].empty()) continue;
			cout<<v[a].back()<<'\n';
		}
		if(b=="front")
		{
			a=read();
			if(v[a].empty()) continue;
			cout<<v[a].front()<<'\n';
		}
		if(b=="size")
		{
			a=read();
			if(v[a].empty()) continue;
			cout<<v[a].size()<<'\n';
		}
	}
	return 0;
}