#include <bits/stdc++.h>

 #define ll long long
 #define ull unsigned long long
 #define pi 3.141592654
 #define NUM 1e18
 #define Mod  1'000'000'007
 #define fixed(n) fixed<<setprecision(n)
 #define cin(v) for(auto &i:v) cin >> i ;
 #define cout(v) for(auto &i:v) cout << i  <<" ";
 #define vowel(x) (x=='e'||x=='a'||x=='i'||x=='o'||x=='u')
 #define small(x) (x>=97&&x<=122)
 #define capital(x) (x>=65&&x<=90)
 #define Tolower(s) transform(s.begin(),s.end(),s.begin(),::tolower);
 #define Toupper(s) transform(s.begin(),s.end(),s.begin(),::toupper);
 #define all(v) ((v).begin()), ((v).end())
 #define allr(v) ((v).rbegin()), ((v).rend())
 #define updmax(a,b) a=max(a,b)
 #define updmin(a,b) a=min(a,b)
 #define ceil(a,b) ((a/b)+(a%b?1:0))
 /* asc -> 1 2 3 ,des -> 3 2 1 */

 /***********************************************************************************/

 using namespace std;

 void Rofyda_Elghadban(){
  #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
   #endif
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
 }

 int partial[1000000]{};
 void solve(){
  int n,m;
  cin>>n>>m;
  vector<int>v(m+1),ans;
  while(n--){
    int l,r;
    cin>>l>>r;
    partial[l]+=1;
    partial[r+1]-=1;
  }
  for(int i=1;i<=m;i++){
    partial[i]+=partial[i-1];
  }
  for(int i=1;i<=m;i++){
    if(partial[i]==0){
      ans.push_back(i);
    }
  }
  if(ans.size()!=0){
    cout<<ans.size()<<"\n";
    cout(ans);
  }else if(ans.size()==0){
    cout<<ans.size()<<"\n"<<" ";
  }




 }


 int main(){
 Rofyda_Elghadban();
 //freopen("input.txt","r",stdin);
 //freopen("output.txt","r",stdout);
 solve();




 return 0;
}