#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <algorithm>
#include <iostream>
#include <queue>
using namespace std;
int flag[10010];
int main()
{
    deque<int >q;
    int n,m,i,k;
    char str[10];
    memset(flag,0,sizeof(flag));
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%s",str);
        if(strcmp(str,"LIN")==0)
        {
            cin>>m;
            q.push_front(m);
        }
        else if(strcmp(str,"RIN")==0)
        {
            cin>>m;
            q.push_back(m);
        }
        else if(strcmp(str,"LOUT")==0)
        {
            if(!q.empty())
                q.pop_front();
            else
                flag[i]=1;
        }
        else if(strcmp(str,"ROUT")==0)
        {
            if(!q.empty())
                q.pop_back();
            else
                flag[i]=1;
        }

    }
        k=q.front();
        q.pop_front();
        cout<<k<<' ';
        while(!q.empty())
        {
            k=q.front();
            q.pop_front();
            cout<<k<<' ';
        }
        cout<<endl;
         for(i=1;i<=n;i++)
        {
            if(flag[i])
                cout<<i<<" "<<"ERROR"<<endl;
        }
}

/**************************************************************
	Problem: 1789
	User: admin
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2116 kb
****************************************************************/