#include <bits/stdc++.h>
using namespace std;
int a, b, c = 0, d = 0, i, j, k = 0, k1 = 0, l = 0, l1 = 0, m[100050], n = 0;
string st, t;
int main() {
  cin >> a >> b;
  c = b;
  for (i = 0; i < a; i++) {
    cin >> m[i];
  }
  m[a] = 1000000001;
  sort(m, m + a);
  k = 0;
  for (i = 0; i <= a; i++) {
    n = m[i];
    for (j = k + 1; j < n; j++) {
      if (b >= j) {
        b = b - j;
        l++;
      } else
        break;
    }
    k = n;
  }
  cout << l << endl;
  k = 0;
  for (i = 0; i <= a; i++) {
    n = m[i];
    for (j = k + 1; j < n; j++) {
      if (c >= j) {
        c = c - j;
        cout << j << " ";
      } else
        break;
    }
    k = n;
  }
  return 0;
}
