#include <fstream>
#include <vector>
#include <cstring>

#define N 100000 + 1
#define M 200000 + 1

using namespace std;

ifstream f ( "ctc.in" );
ofstream g ( "ctc.out" );

vector < int > graph[N];
int k, num, low[N], viz[N], st[N], vsol[N], sol[N], lvl;
bool stiva[N];

void dfs ( int node ){
    viz[node] = low[node] = lvl;
    st[++k] = node;
    stiva[node] = 1;
    for ( int i = 0; i < graph[node].size(); i++ ){
        int new_node = graph[node][i];
        if ( viz[new_node] == 0 ){
            lvl++;
            dfs ( new_node );
            low[node] = min ( low[node], low[new_node] );
        }
        else
            if ( stiva[new_node] == 1 )
                low[node] = min ( low[node], viz[new_node] );
    }
    if ( viz[node] == low[node] ){
        num++;
        sol[num] = sol[num - 1];
        while ( st[k] != node ){
            stiva[st[k]] = 0;
            vsol[ ++ sol[num] ] = st[k];
            k--;
        }
        stiva[st[k]] = 0;
        vsol[ ++ sol[num] ] = st[k];
        k--;
    }
}

int main()
{   int n, m, x, y;
    f >> n >> m;
    for ( int i = 1; i <= m; i++ ){
        f >> x >> y;
        graph[x].push_back ( y );
    }
    lvl = 1;
    for ( int i = 1; i <= n; i++ )
        if ( viz[i] == 0 )
            dfs ( i );
    g << num << '\n';
    for ( int i = 1; i <= num; i++ ){
        for ( int j = sol[i - 1] + 1; j <= sol[i]; j++ )
            g << vsol[j] << ' ';
        g << '\n';
    }
    return 0;
}