#include <fstream>
#include <vector>
#include <stack>

using namespace std;

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

const int nmax = 100000;

vector <int> g[nmax+1];

int level;
int l[nmax+1], ll[nmax+1];
stack <int> s;
bool ins[nmax+1];

vector < vector <int> > sol;

void dfs( int x ) {
    ++ level;
    l[x] = level;
    ll[x] = level;
    s.push(x);
    ins[x] = 1;

    for ( int i = 0; i < int(g[x].size()); ++ i ) {
        int xn = g[x][i];
        if ( l[xn] == 0 ) {
            dfs(xn);
            if ( ll[xn] < ll[x] ) {
                ll[x] = ll[xn];
            }
        } else if ( ins[xn] == 1 ) {
            if ( ll[xn] < ll[x] ) {
                ll[x] = ll[xn];
            }
        }
    }

    if ( ll[x] == l[x] ) {
        int nsol = sol.size()+1;
        sol.resize(nsol);
        sol[nsol-1].resize(0);
        while ( ins[x] == 1 ) {
            int aux = s.top();
            ins[aux] = 0;
            s.pop();
            sol[nsol-1].push_back(aux);
        }
    }
}

int main( ) {
    int n, m;
    fin >> n >> m;
    for ( int i = 1; i <= m; ++ i ) {
        int x, y;
        fin >> x >> y;
        g[x].push_back(y);
    }

    for ( int i = 1; i <= n; ++ i ) {
        if ( l[i] == 0 ) {
            dfs(i);
        }
    }

    fout << sol.size() << "\n";
    for ( int i = 0; i < int(sol.size()); ++ i ) {
        for ( int j = 0; j < int(sol[i].size()); ++j ) {
            fout << sol[i][j] << " ";
        }
        fout << "\n";
    }

    return 0;
}