1822.cpp

// Authored by : unluckyjung
// Co-authored by : -
// http://boj.kr/5cd27ecd3608402da947337b18e2baad
#include <bits/stdc++.h>
using namespace std;

vector<int> A, B;

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);

  int n, m;
  cin >> n >> m;

  int num;
  for (int i = 0; i < n; ++i) {
    cin >> num;
    A.push_back(num);
  }
  for (int i = 0; i < m; ++i) {
    cin >> num;
    B.push_back(num);
  }

  sort(A.begin(), A.end());
  sort(B.begin(), B.end());

  vector<int> ans;
  for (int num : A) {
    if (binary_search(B.begin(), B.end(), num)) continue;
    ans.push_back(num);
  }
  cout << ans.size() << "\n";
  for (int num : ans) cout << num << " ";
}