#include <bits/stdc++.h>   using namespace std;   const long long inf = LLONG_MAX / 2;   const long long MX = 1e5 + 10;   int a[MX];   set<int> s;   vector<int> v;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     int n, m;     cin >> n >> m;     for (long long(i) = (0); (i) <= (n - 1); ++(i)) {       cin >> a[i];       s.insert(a[i]);     }     int num = 1;     while (m >= num) {       if (!s.count(num)) {         m -= num;         v.push_back(num);       }       num++;     }     cout << v.size() << endl;     for (auto it : v) {       cout << it <<    ;     }     return 0;   }   