#include<bits/stdc++.h>
#define int long long
#define N 1919810
using namespace std;
list<int>a[N];
char s[99];
signed main()
{
	int n,i,opt,x,y;
    scanf("%lld",&n);
	while(n--)
	{
		scanf("%s %lld",s,&x);
        //printf("%s\n",s);
		if(strcmp(s,"pop_back")&&!a[x].empty()) a[x].pop_back();
		else if(strcmp(s,"push_back")) scanf("%lld",&y),a[x].push_back(y);
		else if(strcmp("pop_front",s)&&!a[x].empty()) a[x].pop_front();
		else if(strcmp("push_front",s)) scanf("%lld",&y),a[x].push_front(y);
		else if(strcmp(s,"size")) printf("%d\n",a[x].size());
		else if(strcmp("front",s)&&!a[x].empty()) printf("%d\n",a[x].front());
		else if(strcmp("back",s)&&!a[x].empty()) printf("%d\n",a[x].back());
	}
	return 0;
}

不知道为什么就是没有输出，改到 Windows 端甚至没输入完整