#include <bits/stdc++.h>
using namespace std;
int n, m;
set<int> sot;
vector<int> ans;
int main() {
  while (~scanf("%d%d", &n, &m)) {
    sot.clear();
    for (int i = 1; i <= n; ++i) {
      int x;
      scanf("%d", &x);
      sot.insert(x);
    }
    ans.clear();
    for (int i = 1; m >= i; ++i) {
      if (sot.count(i)) continue;
      ans.push_back(i);
      m -= i;
    }
    printf("%d\n", ans.size());
    for (int i = ans.size() - 1; ~i; --i) printf("%d ", ans[i]);
    puts("");
  }
  return 0;
}
