#include <bits/stdc++.h>
using namespace std;
const int inf = 0x3f3f3f3f;
const long long INF = 2e18;
const int N = 1231234;
const int M = 1e9 + 1;
int n, m;
map<int, int> f;
vector<int> a;
int main() {
  while (cin >> n >> m) {
    int i, j;
    for (i = 0; i < n; ++i) {
      int x;
      scanf("%d", &x);
      f[x] = 1;
    }
    for (i = 1; i <= m; ++i) {
      if (f[i] == 0) {
        a.push_back(i);
        m -= i;
      }
    }
    printf("%d\n", a.size());
    for (i = 0; i < a.size(); ++i) printf("%d ", a[i]);
    puts("");
  }
}
