#include <fstream>
#include <cstring>
#define NMAX 5005
using namespace std;

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

int n, m, M[NMAX][NMAX], T[NMAX][NMAX], checked[NMAX], result;

int visitedN[NMAX], visitedT[NMAX];

void DFS(int node, int G[NMAX][NMAX], int vis[NMAX])
{
    vis[node] = 1;
    for(int i = 1; i <= n; i++)
        if(vis[i] == 0 && G[node][i] == 1)
        DFS(i, G, vis);
}

void Strongly_connected_component(int node)
{
    DFS(node, M, visitedN);
    DFS(node, T, visitedT);
    for(int i = 1; i <= n; i++)
        if(visitedN[i] == 1 && visitedT[i] == 1)
        {
            checked[i] = result;
        }
    memset(visitedN, 0, sizeof(visitedN));
    memset(visitedT, 0, sizeof(visitedT));
}

int main()
{
    int i, j, x, y;
    fin >> n >> m;
    for(i = 1; i <= m; i++)
    {
        fin >> x >> y;
        M[x][y] = 1;
        T[y][x] = 1;
    }
    for(i = 1; i <= n; i++)
        if(checked[i] == 0)
        {
            ++result;
            Strongly_connected_component(i);
        }
    fout << result << '\n';
    for(i = 1; i <= result; i++)
    {
        for(j = 1; j <= n; j++)
            if(checked[j] == i)
            fout << j << ' ';
        fout << '\n';
    }
    return 0;
}