#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
using namespace std;

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

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];

void citire()
{
    f >> N >> M;
    for(int i = 1; i <= M; i++)
    {
        int x, y;
        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])
            Dmin[x] = min(Dmin[x], Dmin[y]);
    }
    if(D[x] == Dmin[x])
    {
        nrc++;
        int u;
        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();
    return 0;
}