#include <iostream>
#include <sstream>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <numeric>
#include <vector>

using namespace std;
#define ll long long
void sherry()
{
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}
int main()
{

    sherry();
    ll n, m, count = 0;
    cin >> n >> m;
    ll sum[m + 1]{}, sum2[m + 1]{};
    for (ll i = 1; i <= n; i++)
    {
        ll a, b;
        cin >> a >> b;
        sum[a] += 1;
        sum[b + 1] -= 1;
    }
    for (ll i = 1; i <= m; i++)
    {
        sum2[i] = sum2[i - 1] + sum[i];
        if (sum2[i] == 0)
            count++;
    }
    cout << count << "\n";
    for (ll i = 1; i <= m; i++)
    {
        if (sum2[i] == 0)
            cout << i << " ";
    }
    return 0;
}