#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

#define TASK "lcs"
#define MAXN 50050

int n, a[2 * MAXN], b[2 * MAXN], c[MAXN][2], f[2 * MAXN], q[2 * MAXN];
vector<pair<int, int> > p[2 * MAXN];

int get_max(int x)
{
    int res = 0;
    for ( ; x >= 0; x &= x + 1, x--)
        res = max(res, f[x]);
    return res;
}

void upgrade(int x, int p)
{
    for ( ; x < n; x |= x + 1)
        f[x] = max(f[x], p);
}

void upgrade(int x)
{
    int val = get_max(x - 1);
    if (val + 1 > f[x])
    {
        int l = -1, r = x - 1, m = (l + r) >> 1;
        while (r - l > 1)
        {
            if (get_max(m) == val)
                r = m;
            else
                l = m;
            m = (l + r) >> 1;
        }
        if (val > 0)
            p[x].push_back(make_pair(r, (int)p[r].size() - 1));
        upgrade(x, val + 1);
        q[x] = val + 1;
    }
}

int main()
{
    ifstream cin(TASK".in");
    ofstream cout(TASK".out");

    while (true)
    {
        cin >> n;
        n <<= 1;
        if (!n)
            break;

        for (int i = 0; i < n; ++i)
        {
            cin >> a[i];
            c[a[i]][0] = c[a[i]][1] = -1;
        }
        for (int i = 0; i < n; ++i)
        {
            cin >> b[i];
            if (c[b[i]][1] == -1)
                c[b[i]][1] = i;
            else
                c[b[i]][0] = i;
            f[i] = q[i] = 0;
            p[i].clear();
        }

        for (int i = 0; i < n; ++i)
        {
            upgrade(c[a[i]][0]);
            upgrade(c[a[i]][1]);
        }

        int ans = get_max(n - 1);
        cout << ans << endl;
        vector<int> ansp;
        pair<int, int> cur;
        for (int i = n - 1; ; --i)
            if (q[i] == ans)
            {
                ansp.push_back(b[i]);
                cur = p[i][p[i].size() - 1];
                break;
            }
        for (int k = ans; ; cur = p[cur.first][cur.second])
        {
            ansp.push_back(b[cur.first]);
            if (cur.second == -1 || p[cur.first].size() == 0)
                break;
        }
        for (vector<int>::reverse_iterator it = ansp.rbegin(); it != ansp.rend(); ++it)
            cout << *it << " ";
        cout << endl;
    }

    return 0;
}