#include <iostream>

using namespace std;

int n,m,a[101][101],x,y,v[101],c;

int main()
{
    cin >> n >> m;
    for(int i=1;i<=m;i++)
    {
        cin >> x >> y;
        a[x][y]=1;
    }
    for(int i=1;i<=n;i++)
    {
        int suma1=0,suma2=0;
        for(int j=1;j<=n;j++)
        {
            suma1=suma1+a[i][j];
            suma2=suma2+a[j][i];
        }
        if(suma1==suma2)
            v[++c]=i;
    }
    cout << c << endl;
    for(int i=1;i<=c;i++)
        cout << v[i] << " ";

    return 0;
}