#include <bits/stdc++.h>
using namespace std;
struct dupe {
  string name;
  string ip;
};
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n, m;
  cin >> n >> m;
  priority_queue<int, vector<int>, greater<int> > anan;
  priority_queue<int, vector<int>, greater<int> > nana;
  for (int i = 0; i < n; i++) {
    int c;
    cin >> c;
    anan.push(c);
    nana.push(c);
  }
  int cnt = 0;
  int mm = m;
  for (int i = 1; i < n, m >= 0; i++) {
    if (i != anan.top()) {
      m = m - i;
      if (m < 0) {
        break;
      }
      cnt++;
    } else {
      anan.pop();
    }
  }
  m = mm;
  cout << cnt << endl;
  for (int i = 1; i < n, m >= 0; i++) {
    if (i != nana.top()) {
      m = m - i;
      if (m < 0) {
        break;
      }
      cout << i << " ";
    } else {
      nana.pop();
    }
  }
}
