#include<cstdio>

 #include<cstring>

 #include<string>

 #include<cmath>

 #include<iostream>

 #include<algorithm>

 #include<map>

 #include<set>

 #include<queue>

 #include<vector>

 using namespace std;

 typedef long long ll;

 typedef unsigned int uint;

 typedef unsigned long long ull;

 typedef pair<int,int> PII;

 typedef vector<int> VI;

 #define fi first

 #define se second

 #define MP make_pair

 const int N=;

 int a[N],n,m;

 int read()

 {

    int v=,f=;

    char c=getchar();

    while(c<||<c) {if(c=='-') f=-; c=getchar();}

    while(<=c&&c<=) v=(v<<)+v+v+c-,c=getchar();

    return v*f;

 }

 int main()

 {

   //freopen("1.in","r",stdin);

   //freopen("1.out","w",stdout);

   scanf("%d%d",&n,&m);

   for(int i=;i<=n;i++)

   {

       int x,y;

     scanf("%d%d",&x,&y);

     for(int j=x;j<=y;j++) a[j]=;

   }

   int ans=;

   for(int i=;i<=m;i++) ans+=a[i];

   printf("%d\n",m-ans);

   for(int i=;i<=m;i++)

    if(!a[i]) printf("%d ",i);

   return ;

 }