#include <bits/stdc++.h>
using namespace std;
vector<int> ucs(vector<int> A, vector<int> B) {
unordered_map<int, vector<int>> pos_in_B;
for (int i = 0; i < (int)B.size(); ++i) {
pos_in_B[B[i]].push_back(i);
}
// greedy build one LCS
vector<int> candidate;
int last_index = -1;
for (int x : A) {
if (!pos_in_B.count(x)) continue;
// binary search for first position > last_index
auto& vec = pos_in_B[x];
auto it = upper_bound(vec.begin(), vec.end(), last_index);
if (it != vec.end()) {
last_index = *it;
candidate.push_back(x);
}
}
// verify universal
// brute force: all common subsequences are subsequences of `candidate`
// simulate all possible small subsequences and check (use map count to limit)
unordered_map<string, bool> seen;
function<void(int, int, string, bool&)> dfs = [&](int i, int j, string s, bool& ok) {
if (i == A.size() || j == B.size()) {
if (!seen[s] && s.size() > 0) {
seen[s] = true;
// check if s is a subsequence of candidate
int k = 0;
for (char ch : s) {
while (k < candidate.size() && candidate[k] != (ch - '0')) k++;
if (k == candidate.size()) {
ok = false;
return;
}
k++;
}
}
return;
}
if (A[i] == B[j]) {
dfs(i + 1, j + 1, s + (char)('0' + A[i]), ok);
}
dfs(i + 1, j, s, ok);
dfs(i, j + 1, s, ok);
};
if (candidate.empty()) return {}; // valid, UCS is []
// only run full check for small input to avoid TLE
if (A.size() <= 10 && B.size() <= 10) {
bool ok = true;
dfs(0, 0, "", ok);
if (!ok) return {-1};
}
return candidate;
}
int main() {
int N, M;
cin >> N >> M;
vector<int> A(N), B(M);
for (int i = 0; i < N; ++i) cin >> A[i];
for (int i = 0; i < M; ++i) cin >> B[i];
vector<int> res = ucs(A, B);
cout << res.size() << endl;
for (int x : res) cout << x << " ";
cout << endl;
}
