#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);

	int n, m;
    cin >> n >> m;

    bool exists[200000] = { false };

    int curr;

    for(int i = 0; i < n; i++) {
        cin >> curr;
        exists[curr] = true;
    }

    int maxHole = 0;
    int maxHoleIndex = 0;
    int streak = 0;

    for(int i = 0; i < 2 * m; i++) {
        if (!exists[i % m]) {
            streak++;
        }
        else {
            if (streak > maxHole) {
                maxHole = streak;
                maxHoleIndex = i % m;
            }
            streak = 0;
        }
    }

    int commandN = m - 1 - maxHole;
    cout << commandN << endl;

    for(int i = 0; i < commandN; i++) {
        cout << ((maxHoleIndex + i) % m) << " ";
    }

}