#include <iostream>
#include <cstdio>
#include <vector>
#include <iterator>
#include <stack>
using namespace std;

const int MAXN = 100000, MAXM = 200000;

int N, M;
vector < vector <int> > G, GT;

void readData()
{
    freopen("ctc.in","r",stdin);
    scanf("%d %d",&N,&M);

    for(int i = 0 ; i <= N; i++)
    {
        vector <int> aux;
        G.push_back(aux);
        GT.push_back(aux);
    }

    for(int i = 1; i <= M; i++)
    {
        int x, y;
        scanf("%d %d",&x,&y);
        G[x].push_back(y);
    }
}

vector <int> stiva;
int vizitat[MAXN+1];

void dfs(int nod)
{
    vizitat[ nod ] = 1;

    for(int i = 0; i < G[ nod ].size(); i++)
    {
        int nextNode = G[ nod ][ i ];

        if( vizitat[ nextNode ] == 0 )
            dfs( nextNode );
    }

    stiva.push_back( nod );
}

void construiesteGrafTranspus()
{
    for(int i = 0; i <= N; i++)
        for(int j = 0 ; j < G[ i ].size(); j++)
        {
            int node = G[ i ][ j ];
            GT[ node ].push_back( i );
        }
}

vector <int> deAfisat;

void dfsTranspus(int nod, int k)
{
    vizitat[ nod ] = 1;
    deAfisat.push_back( nod );
    for(int i = 0; i < GT[ nod ].size(); i++)
    {
        int nextNode = GT[ nod ][ i ];

        if( vizitat[ nextNode ] == 0 )
            dfsTranspus( nextNode, k );
    }

}

int counter = 0;



int main()
{
    readData();

    for(int i = 1; i <= N; i++)
        if( vizitat[ i ] == 0 )
            dfs( i );

    for(int i = 1; i <= N; i++)
        vizitat[ i ] = 0;

    construiesteGrafTranspus();

    while( stiva.empty() == false )
    {
        if( vizitat[ stiva[ stiva.size() - 1 ] ] == 0 )
        {
            counter++;
            dfsTranspus( stiva[ stiva.size() - 1 ], counter );
            deAfisat.push_back(0);
        }
        else stiva.pop_back();
    }

    freopen("ctc.out","w",stdout);

    printf("%d\n",counter);
    /*
    for(int i = 1; i <= counter; i++)
    {
        for(int j = 1; j <= N && cate[ i ]; j++)
        {
            if( c[ j ] == i )
            {
                printf("%d ",j);
                cate[ i ]--;
            }
        }
        printf("\n");
    }*/

    int currentComp = 1;

    int index = 0;

    for(int i = 1; i <= counter; i++)
    {
        while( deAfisat[ index ] != 0 )
        {
            //cout<<deAfisat[ index ]<<' ';
            printf("%d ",deAfisat[ index ]);
            index++;
        }
        index++;
        //cout<<endl;
        printf("\n");
    }


    return 0;
}