#include <iostream>
#include <algorithm>
#include <vector>
#include <set>

using namespace std;

int main()
{
    int n, m, i, space=0, start=0, end=0, temp;
	vector<int> Vfreq;
	set<int> freq;
	cin >> n >> m;
	for (i = 0; i < n; i++)
	{
		cin >> temp;
		freq.insert(temp);
	}
	Vfreq.assign(freq.begin(), freq.end());
	sort(Vfreq.begin(), Vfreq.end());
	

	space = (m + Vfreq[0]) - Vfreq[Vfreq.size() - 1];
	start = Vfreq[0], end = Vfreq[Vfreq.size() - 1];

	for (i = 1; i < Vfreq.size(); i++)
	{
		if (Vfreq[i]-Vfreq[i-1] > space)
		{
			space = Vfreq[i] - Vfreq[i - 1];
			start = Vfreq[i], end = Vfreq[i - 1];
		}
	}

	cout << m - space << '\n';
	temp = start;
	for (i = 0; i < m - space; i++)
	{
		cout << temp << ' ';
		temp = (temp + 1) % m;
	}
}