#include <bits/stdc++.h>

#define MaxN 100005
#define MaxM 200005

std::ifstream InFile("ctc.in");
std::ofstream OutFile("ctc.out");

// Liste de adiacenta alocate static
int N, M;
std::list <int> Adc[MaxN];
std::list <int> AdcT[MaxN];
std::vector <int> CTCMembers[MaxN];
int CTCCount;

int Mark[MaxN];

void DFS(int Node, std::list <int> Adc[], int Value) {
    Mark[Node] += Value;

    for (auto it:Adc[Node]) {
        if(Mark[it] < Value)
            DFS(it, Adc, Value);
    }
}

void FindCTC(int Index) {
    DFS(Index, Adc, 1);
    DFS(Index, AdcT, 2);

    for (int i=0; i<N; i++) {
        if(Mark[i+1] == 3)
            Mark[i+1] = 4,
            CTCMembers[CTCCount].push_back(i+1);
        else Mark[i+1] = 0;
    }   CTCCount ++;
}

void Citire() {
    InFile >> N >> M ;
    for (int i=0, x, y; i<M; i++) {
        InFile >> x >> y;
        Adc[x].push_back(y);
        AdcT[y].push_back(x);
    }
}

void Rezolvare() {
    for (int i=0; i<N; i++)
        if (!Mark[i+1])
            FindCTC(i+1);

    OutFile << CTCCount << '\n';
    for (int i=0, j; i<CTCCount; i++) {
        for (j=0; j<CTCMembers[i].size(); j++)
            OutFile << CTCMembers[i][j] << ' ' ;
        OutFile << '\n';
    }
}

int main()
{
    Citire();
    Rezolvare();

    return 0;
}