#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, i, x;
  cin >> n >> m;
  set<int> a, b;
  for (i = 0; i < n; i++) {
    cin >> x;
    a.insert(x);
  }
  for (i = 1; i <= m; i++) {
    if (a.find(i) == a.end()) {
      b.insert(i);
      m = m - i;
    }
  }
  cout << b.size() << endl;
  for (auto j : b) cout << j << " ";
}
