#include <bits/stdc++.h>
#define ios ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define file(s) if (fopen(s".in", "r")) freopen(s".in", "r", stdin), freopen(s".out", "w", stdout)
#define all(a) a.begin() , a.end()
#define F first
#define S second
using namespace std;
using ll = long long;
const ll N = 2e5+5 , inf = 2e9 + 7;
const ll INF = 1e18 ,   mod = 1e9+7;
int a[N] , b[N];
vector<int> ucs(vector<int> A, vector<int> B) {
	int n = A.size() , lastA = -1 , lastB = -1;
	vector<int> vec;
	for(int i = 0; i < n; i++) a[i] = b[i] = -1;
	for(int i = 0; i < n; i++){
		if(A[i] == B[i]){
			vec.push_back(A[i]);
			continue;
		}
		a[A[i]] = i;
		b[B[i]] = i;
		if(b[A[i]] > lastB && a[B[i]] > lastA){
			return vector<int>({-1});
		}
		if(b[A[i]] > lastB) vec.push_back(A[i]) , lastA = i;
		if(a[B[i]] > lastA) vec.push_back(B[i]) , lastB = i;
	}
	return vec;
}
// int main() {
  // int N, M;
  // assert(2 == scanf("%d%d", &N, &M));
  // std::vector<int> A(N), B(M);
  // for (int i = 0; i < N; i++)
    // assert(1 == scanf("%d", &A[i]));
  // for (int j = 0; j < M; j++)
    // assert(1 == scanf("%d", &B[j]));
  // fclose(stdin);
// 
  // std::vector<int> R = ucs(A, B);
// 
  // int T = (int)R.size();
  // printf("%d\n", T);
  // for (int i = 0; i < T; i++)
    // printf("%s%d", (i == 0 ? "" : " "), R[i]);
  // printf("\n");
  // fclose(stdout);
// 
  // return 0;
// }
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