#include <iostream>
#include <algorithm> // for sort, mainly
#include <vector>
#include <map>
#include <set>
#include <cmath>
#include <array>
#include <string>
#include <cstdio>
#include <iterator>
#include <unordered_set>
#include <cstdint> // for int64_t, int32_t, etc
#include <queue>
#include <stack>
#include <deque>
#include <numeric> // gcd, lcm
#include <fstream>
#include <bitset> // for bitset
#include <iomanip>
#include <cassert> // for set with custom ordering
#include <type_traits> // for set with custom ordering
#include <utility> // for swap, forward, etc
using namespace std;

#pragma GCC optimize("O2")
// #pragma GCC optimize("O1","O2","O3","Ofast","unroll-loops")
// #pragma GCC target("sse","sse2","sse3","sse4.1","sse4.2","avx","avx2","fma")

template<typename A, typename B> ostream& operator<<(ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }
template<typename T_container, typename T = typename enable_if<!is_same<T_container, string>::value, typename T_container::value_type>::type> ostream& operator<<(ostream &os, const T_container &v) { os << '{'; string sep; for (const T &x : v) os << sep << x, sep = ", "; return os << '}'; }
void dbg_out() { cout << endl; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cout << ' ' << H; dbg_out(T...); }
#ifdef LOCAL
#define dbg(...) cout << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#else
#define dbg(...)
#endif

/*

notes:

int64_t
stoi(string s) -> string to int
to_string() -> int (or else) to string

vector declaration:
vector<ll> v(n, 0)
vector<vector<ll>> v(n, vector<ll>(n, 0));

{if statement} ? {truth value} : {false value}

#ifdef LOCAL
    freopen("in.txt","r",stdin);
    freopen("out.txt","w",stdout);
#endif

std::lcm(ll a, ll b), std::gcd(int a, int b)

cout << fixed << setprecision(n);

set with custom ordering
set<ll, decltype(&cmp)> qu(cmp);

*/

typedef int64_t ll;

void solve() {

	ll n, m;
	cin >> n >> m;

	set<ll> s;
	for(ll i = 0; i < n; i++) 
	{
		ll h;
		cin >> h;
		s.insert(h);
	}

	// minden ertekre megnezzuk, hogy mennyibe kerulne
	// hogy "korbemenjen"
	// vagyis az elotte levo nalanal kisebb ertekik visszajusson
	// ezeknek a minimuma a valasz

	if(s.size() == 1) {

		cout << "0";
		return;

	}

	ll sm = *s.begin();
	ll lg = *s.rbegin();

	ll mx = m + 1;
	ll num = 0;
	ll pfin = 0;
	for(const auto & x : s) {

		// ha a legkisebb, akkor csak nezzuk hogy a legnagyobbig

		ll curr = m+1;	

		ll ph = 0;

		if(x == sm) {

			// akkor a legnagyobbig megy
			curr = lg - x;
		}else{

			ll pv = *prev(s.lower_bound(x));
			ph =pv;

			ll between = x - pv;
			curr = m - between;

		}

		if(curr < mx) {
			mx = curr;
			num = x;
			pfin = ph;
		}

	}

	cout << mx << "\n";
	if(num == sm) {
		for(ll i = sm; i < lg; i++) {
			cout << i << " ";
		}
	}else{

		for(ll i = num; i < m; i++) {
			cout << i << " ";
		}
		for(ll i = 0; i < pfin; i++) {
			cout << i << " ";
		}

	}

}

int main()
{
	std::ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);

	solve();

	return 0;
}