#include <bits/stdc++.h>
using namespace std;
int a[100050];
int ans[100050];
int main() {
  int n, m;
  while (~scanf("%d%d", &n, &m)) {
    for (int i = 0; i < n; i++) {
      scanf("%d", &a[i]);
    }
    sort(a, a + n);
    int now = 0;
    int cont = 0;
    for (int i = 1; i <= 1000000; i++) {
      if (a[now] != i || now >= n) {
        if (m >= i) {
          m -= i;
          ans[cont++] = i;
        } else
          break;
      }
      if (a[now] == i) {
        while (1) {
          if (a[now] == i) now++;
          if (now >= n)
            break;
          else
            break;
        }
      }
    }
    printf("%d\n", cont);
    for (int i = 0; i < cont; i++) {
      printf("%d ", ans[i]);
    }
    printf("\n");
  }
}
