#include <fstream>
#include <vector>
#include <stack>
using namespace std;

ifstream is("ctc.in");
ofstream os("ctc.out");

int n, m;
int x, y, k, nr;
vector<vector<int>> G, GT, Sol;
vector<bool> s;
stack<int> Q;

void Df(int k);
void Dft( int k, int nr );

int main()
{
    is >> n >> m;
    G.resize(n+1);
    GT.resize(n+1);
    Sol.resize(n+1);
    for ( int i = 1; i <= m; i++ )
    {
        is >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
    s = vector<bool>(n+1);
    for ( int i = 1; i <= n; i++ )
        if ( !s[i] )
            Df(i);
    s.assign(n+1, false);
    while( !Q.empty() )
    {
        k = Q.top();
        Q.pop();
        if ( !s[k] )
        {
            nr++;
            Dft(k, nr);
        }
    }
    os << nr << '\n';
    for ( int i = 1; i <= nr; i++ )
    {
        for ( vector<int>::iterator it = Sol[i].begin(); it != Sol[i].end(); ++it )
            os << *it << ' ';
        os << '\n';
    }
    is.close();
    os.close();
    return 0;
}

void Df( int k )
{
    s[k] = true;
    for ( vector<int>::iterator it = G[k].begin(); it != G[k].end(); ++it )
        if( !s[*it] )
            Df(*it);
    Q.push(k);
}

void Dft(int k, int nr)
{
    s[k] = true;
    Sol[nr].push_back(k);
    for ( vector<int>::iterator it = GT[k].begin(); it != GT[k].end(); ++it )
        if( !s[*it] )
            Dft(*it, nr);

}