#include <bits/stdc++.h>
using namespace std;
int a[1000000];
int main() {
  int n, m;
  cin >> n >> m;
  set<int> st;
  for (int i = 0; i < n; i++) {
    int first;
    cin >> first;
    st.insert(first);
  }
  int cnt = 0;
  for (int i = 1; m; i++) {
    if (st.find(i) != st.end()) continue;
    if (i > m) break;
    m -= i;
    a[cnt++] = i;
  }
  cout << cnt << endl;
  for (int i = 0; i < cnt; i++) cout << a[i] << " ";
}
