#include <bits/stdc++.h>
#define NMAX 100005

using namespace std;

ifstream fin ("ctc.in");
ofstream fout ("ctc.out");

stack < int > s;
vector < int > v1[NMAX], v2[NMAX], r[NMAX];
bitset < NMAX > viz1, viz2;
int nr;

void dfs1 ( int nod );
void dfs2 ( int nod );

int main()
{
    int n, m, x, y, i, j;

    fin >> n >> m;
    while ( m-- )
    {
        fin >> x >> y;
        v1[x].push_back ( y );
        v2[y].push_back ( x );
    }

    for ( i = 1 ; i <= n ; i++ ) if ( viz1[i] == 0 ) dfs1 ( i );

    while ( s.empty() == 0 )
    {
        if ( viz2[s.top()] == 0 )
        {
            nr++;
            dfs2 ( s.top() );
        }

        s.pop();
    }

    fout << nr << '\n';
    for ( i = 1 ; i <= nr ; i++ )
    {
        for ( j = 0 ; j < r[i].size() ; j++ ) fout << r[i][j] << ' ';
        fout << '\n';
    }

    return 0;
}

void dfs1 ( int nod )
{
    int i;

    viz1[nod] = 1;
    for ( i = 0 ; i < v1[nod].size() ; i++ ) if ( viz1[v1[nod][i]] == 0 ) dfs1 ( v1[nod][i] );

    s.push ( nod );
}

void dfs2 ( int nod )
{
    int i;

    viz2[nod] = 1;
    for ( i = 0 ; i < v2[nod].size() ; i++ ) if ( viz2[v2[nod][i]] == 0 ) dfs2 ( v2[nod][i] );
    r[nr].push_back ( nod );
}