#include <bits/stdc++.h>

using namespace std;
ifstream f("sortaret.in");
ofstream g("sortaret.out");
int q,viz[100005],i,n,x,y,sortare[100005],m;
vector <int> v[100005];
void dfs (int x)
{
    viz[x]=1;
    for (int i=0;i<v[x].size();i++)
    {
        if (viz[v[x][i]]==0)
        {
            dfs(v[x][i]);
        }
    }
    sortare[++q]=x;
}
int main()
{
    f>>n>>m;
    for (i=1;i<=m;i++)
    {
        f>>x>>y;
        v[x].push_back(y);
    }
    for (i=1;i<=n;i++)
    {
        if (viz[i]==0)
        {
            dfs(i);
        }
    }
    g<<q<<'\n';
    for (i=q;i>=1;i--)
    {
        g<<sortare[i]<<" ";
    }
    return 0;
}