#include <bits/stdc++.h>
using namespace std;
int main() {
  set<long long> s;
  long long n, m, x, i, sum = 0, ans = 0, a[100000];
  cin >> n >> m;
  for (i = 1; i <= n; i++) {
    cin >> x;
    s.insert(x);
  }
  for (i = 1; i <= m; i++) {
    if (s.find(i) == s.end()) {
      sum = sum + i;
      if (sum <= m)
        a[++ans] = i;
      else
        break;
    }
  }
  cout << ans << endl;
  for (i = 1; i <= ans; i++) cout << a[i] << " ";
}
