既然没人发题解，那就我来

#include <bits/stdc++.h>
#define ll long long
#define re register int
using namespace std;
int n, x, a[10005], cnt;
string s;
deque<int> dq;
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cin >> n;
    for (re i = 1; i <= n; i++)
    {
        cin >> s;
        if (s == "LIN")
        {
            cin >> x;
            dq.push_front(x);
        }
        else if (s == "RIN")
        {
            cin >> x;
            dq.push_back(x);
        }
        else if (s == "ROUT")
        {
            if (dq.empty()) a[++cnt] = i;
            else dq.pop_back();
        }
        else if (s == "LOUT")
        {
            if (dq.empty()) a[++cnt] = i;
            else dq.pop_front();
        }
    }
    for (auto b : dq) cout << b << " ";
    cout << "\n";
    for (re i = 1; i <= cnt; i++) cout << a[i] << " ERROR\n";
    return 0;
}