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

using namespace std;
const int NMAX = 100000;

int N, M, nrc;

vector<int> G[NMAX + 1], CTC[NMAX + 1];
int D[NMAX + 1], Dmin[NMAX + 1], Timp = 0;
stack<int> S;
bool inSt[NMAX + 1];

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

void citire()
{
    int x, y;
    f >> N >> M;
    for(int i = 1; i <= M; i++)
    {
        f >> x >> y;
        G[x].push_back(y);
    }
}

void DFS(int x)
{
    D[x] = ++Timp;
    Dmin[x] = D[x];
    S.push(x);
    inSt[x] = 1;
    for(auto &y : G[x])
    {
        if(D[y] == 0)
        {
            DFS(y);
            Dmin[x] = min(Dmin[x], Dmin[y]);
        }
        else
        {
            if(inSt[y] == 1)
                Dmin[x] = min(Dmin[x], D[y]);
        }
    }
    //
    if(Dmin[x] == D[x])
    {
        int u;
        nrc++;
        do
        {
            u = S.top();
            CTC[nrc].push_back(u);
            S.pop();
            inSt[u] = 0;
        }
        while(x != u);
    }
}

void afisare()
{
    g << nrc << '\n';
    for(int i = 1; i <= nrc; ++i)
    {
        for(auto &x : CTC[i])
            g << x << ' ';
        g << '\n';
    }
}

int main()
{
    citire();
    for(int i = 1; i <= N; i++)
    {
        if(D[i] == 0)
            DFS(i);
    }
    afisare();
    f.close();
    g.close();
    return 0;
}