#include <iostream>
#include <fstream>
#include <vector>
#include <bitset>
#define MAX_N 100005

using namespace std;

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

vector <int> G[MAX_N], GT[MAX_N], CTC[MAX_N/2];
int Stack[MAX_N], top, nrc;
bitset <MAX_N> viz;

void dfs(int nod)
{
    viz[nod] = 1;
    for(int i = 0; i < G[nod].size(); i++)
        if(viz[G[nod][i]] == 0)
            dfs(G[nod][i]);
    Stack[++top] = nod;
}

void dfst(int nod)
{
    viz[nod] = 0;
    CTC[nrc].push_back(nod);
    for(int i = 0; i < GT[nod].size(); i++)
        if(viz[GT[nod][i]] == 1)
            dfst(GT[nod][i]);
}

int main()
{
    int N, M, i, x, y;
    f >> N >> M;
    for(i = 1; i <= M; i++)
    {
        f >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
    for(i = 1; i <= N; i++)
        if(viz[i] == 0)
            dfs(i);
    for(i = N; i >= 1; i--)
        if(viz[Stack[i]] == 1)
        {
            nrc++;
            dfst(Stack[i]);
        }
    g<<nrc<<endl;
    for(i = 1; i <= nrc; i++)
    {
        for(int j = 0; j < CTC[i].size(); j++)
            g<<CTC[i][j]<<" ";
        g<<endl;
    }
    return 0;
}