#include <bits/stdc++.h>
#define NMAX 100010
using namespace std;
ifstream f ("ctc.in") ;
ofstream g ("ctc.out") ;
int N , M , x , y , cnt = 0;
stack <int> st;
bool viz[NMAX] ;
vector <int> G[NMAX] , GT[NMAX] , CTC[NMAX];
void DFS (int nod)
{
    viz[nod] = true ;
    int lg = G[nod].size() ;
    for (int i = 0 ; i < lg;  ++i)
    {
        int vec = G[nod][i] ;
        if (!viz[vec]) DFS(vec);
    }

    st.push(nod) ;
}
void DFST(int nod)
{
    viz[nod] = false;
    int lg = GT[nod].size() ;
    for (int i = 0 ; i < lg ; ++i)
    {
        int vec = GT[nod][i];
        if (viz[vec])DFST(vec) ;
    }

    CTC[cnt].push_back(nod) ;
}
int main()
{
    f >> N >> M  ;
    for (int i = 1 ; i <= M ; ++i)
    {
        f >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }

    for (int nod = 1;  nod <= N ; ++nod)
        if (!viz[nod]) DFS(nod) ;

    while (!st.empty())
    {
        int nod = st.top();
        st.pop() ;
        if (viz[nod]) {cnt ++ ; DFST(nod) ;}
    }

    g << cnt << '\n' ;
    for (int i = 1 ; i <= cnt ; ++i)
    {
        int lg = CTC[i].size();
        for (int j = 0 ; j < lg ; ++j) g << CTC[i][j] << ' ' ;
        g << '\n' ;
    }
    f.close();
    g.close();
    return 0 ;
}