#include <bits/stdc++.h>
using namespace std;
set<int> X;
vector<int> A;
int main() {
  int temp;
  int N, M;
  scanf("%d %d", &N, &M);
  while (N--) scanf("%d", &temp), X.insert(temp);
  for (int i = 1; M - i >= 0; ++i) {
    if (X.find(i) != X.end()) continue;
    M -= i;
    A.push_back(i);
  }
  printf("%d\n", (int)A.size());
  for (int i = 0; i < A.size(); ++i) printf("%d ", A[i]);
  printf("\n");
  return 0;
}
