#include <bits/stdc++.h>   using namespace std;   int main() {     vector<long long> no;     long long int n, m, s = 0, a[100000], l = 1, i;     cin >> n >> m;     for (i = 1; i <= n; i++) cin >> a[i];     sort(a + 1, a + 1 + n);     for (i = 1; i <= m; i++) {       if (a[l] == i)         l++;       else {         s += i;         if (s <= m)           no.push_back(i);         else           break;       }     }     cout << no.size() << endl;     for (int j = 0; j < no.size(); j++) cout << no[j] <<    ;     return 0;   }   