#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-10;
const int inf = 0x3f3f3f3f, N = 2e5 + 10;
map<int, int> mp;
int main() {
  int n, sum;
  while (cin >> n >> sum) {
    int x;
    while (n--) {
      scanf("%d", &x);
      mp[x] = 1;
    }
    int i = 1, m = 0;
    vector<int> ans;
    while (sum >= i) {
      if (mp[i] == 0) ans.push_back(i), sum -= i, m++;
      ;
      i++;
    }
    printf("%d\n", m);
    for (int i = 0, sz = ans.size(); i < sz; i++) printf("%d ", ans[i]);
  }
}
