//#include <iostream>
#include <bits/stdc++.h>
using namespace std;
int s[100005],p[100005],n,m,nrc,ctc[100005],ss;
bool ok;
vector <int >v[100005];
ifstream in("ctc.in");
ofstream out("ctc.out");
void citire()
{
    in>>n>>m;
    for(int i=0;i<m;i++)
    {
        int x,y;
        in>>x>>y;
        v[x].push_back(y);
    }

}
void dfs1(int x)
{
    s[x]=1;
    for(int i=0;i<v[x].size();i++)
    {
        int vecin=v[x][i];
        if(s[vecin]==0)
            dfs1(vecin);
    }
}
void dfs2(int x)
{
    p[x]=1;
    for(int i=1;i<=n;i++)
        if(!v[i].empty())
        for(int j=0;j<v[i].size();j++)
        {
            int vecin=v[i][j];
            if(vecin==x && p[i]==0)
                dfs2(i);
        }


}
int main()
{
   citire();
   for(int i = 1 ; i <= n ; ++i)
        if(ctc[i] == 0)
        {
            for(int j = 1; j <= n ; ++j)
                s[j] = p[j] = 0;
            nrc ++;
            dfs1(i); dfs2(i);
            for(int j = 1; j <= n ; ++j)
                if(s[j] == 1 && p[j] == 1)
                {
                    ctc[j] = nrc;
                    ok=1;
                }

        }
        if(ok==1)
        {
             out<<nrc<<"\n";
              ss=1;
              for(int j = 1; j <= n ; ++j)
                if(ctc[j]==ss)
                out<<j<<" ";
              else
              {
                  out<<"\n";
                  ss++;
                  j--;
              }

        }
        else
            out<<0;



    return 0;
}