grade2

#include <bits/stdc++.h>

using namespace std;
int de[101];///de[i]=gradul exterior al lui i
int di[101];///di[i]=gradul interior al lui i
int n;
int main()
{
    int i,j,m;
    cin>>n>>m;
    while(m--)
    {
        cin>>i>>j;
        de[i]++;
        di[j]++;
    }
    m=0;
    for(i=1;i<=n;i++)
        if(de[i]==di[i])m++;
    cout<<m<<endl;
    for(i=1;i<=n;i++)
        if(de[i]==di[i])cout<<i<<" ";
    return 0;
}