#include <fstream>
#include <vector>
#define f in
#define g out

using namespace std;
ifstream in ( "ctc.in" );
ofstream out( "ctc.out" );
int n, m, i, x, y, nivel, ctc;
int niv[100100], low[100100], fr[100100];
vector<int> L[100100], sol[100100], s;

void dfs( int nod ){
    
    nivel++;
    niv[nod] = nivel;
    low[nod] = nivel;
    s.push_back(nod);
    fr[nod] = 1;
    
    for ( auto vecin: L[nod] )
        if ( !niv[vecin] ){
            dfs(vecin);
            low[nod] = min ( low[nod], low[vecin] );
        } else if ( fr[nod] )
            low[nod] = min ( low[nod], low[vecin] );
    
    if ( niv[nod] == low[nod] ){
        ctc++;
        x = nod;
        do {
            x = s.back();
            sol[ctc].push_back(x);
            fr[x] = 0;
            s.pop_back();
        } while ( x != nod );
    }
    
}

int main() {
    
    f>>n>>m;
    for ( i=1; i <= m; i++ ){
        f>>x>>y;
        L[x].push_back(y);
    }
    
    for ( i=1; i <= n; i++ )
        if ( !niv[i] )
            dfs(i);
    
    g<<ctc<<"\n";
    for ( i=1; i <= ctc; i++, g<<"\n" )
        for ( auto nod: sol[i] )
            g<<nod<<" ";
    return 0;
}