#include <bits/stdc++.h>
using namespace std;
const long long N = 2e4;
const long long mod = 1e9 + 7;
const long long INF = 1e9 + 1;
const long double eps = 1e-9;
const long double pi = acos(-1.0);
map<long long, long long> used;
vector<long long> v;
long long n, m;
int main() {
  ios_base::sync_with_stdio(0);
  cout.tie(0);
  cin.tie(0);
  cin >> n >> m;
  for (long long i = 1; i <= n; ++i) {
    long long x;
    cin >> x;
    ++used[x];
  }
  for (long long i = 1; i <= (long long)1e9; ++i) {
    if (m - i < 0) {
      break;
    }
    if (!used[i]) {
      v.push_back(i);
      m -= i;
    }
  }
  cout << (long long)v.size() << "\n";
  for (long long i : v) {
    cout << i << " ";
  }
  return 0;
}
