#include <bits/stdc++.h>

using namespace std;

const int NMAX = 1e5;

vector <int> edges[NMAX + 1];
vector <vector <int>> comp;
int found_time[NMAX + 1], min_found[NMAX + 1];

bool onStack[NMAX + 1];
stack <int> st;

int t = 0;

void dfs( int node ) {
    found_time[node] = min_found[node] = ++t;
    onStack[node] = true;
    st.push( node );
    for ( auto vec : edges[node] ) {
        if ( !found_time[vec] ) {
            dfs( vec );
            min_found[node] = min( min_found[node], min_found[vec] );
        } else if ( onStack[vec] ) {
            min_found[node] = min( min_found[node], found_time[vec] );
        }
    }

    if ( min_found[node] == found_time[node] ) {
        vector <int> componenta;
        int aux;
        do {
            aux = st.top();
            componenta.push_back( aux );
            onStack[aux] = false;
            st.pop();
        } while ( aux != node );
        comp.push_back( componenta );
    }
}
int main() {
    ifstream fin("ctc.in");
    ofstream fout("ctc.out");
    int n, m, i, a, b;
    fin >> n >> m;
    for ( i = 0; i < m; i ++ ) {
        fin >> a >> b;
        edges[a].push_back( b );
    }
    for ( int i = 1; i <= n; i ++ ) if ( !found_time[i] ) dfs( i );
    fout << comp.size() << '\n';
    for ( auto componenta : comp ) {
        for ( auto node : componenta ) fout << node << ' ';
        fout << '\n';
    }
    return 0;
}