#include <bits/stdc++.h>
using namespace std;
const int N = 100010;
int n, m;
int polje[N];
int p = 1, pos;
int sol[10000010];
int spos;
int main() {
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> polje[i];
  }
  sort(polje, polje + n);
  while (1) {
    if (p == polje[pos]) {
      p++;
      pos++;
      continue;
    }
    if (p > m) {
      break;
    }
    m -= p;
    sol[spos] = p;
    spos++;
    p++;
  }
  cout << spos << endl;
  for (int i = 0; i < spos; i++) {
    cout << sol[i] << ' ';
  }
}
