#include <bits/stdc++.h>
#define NMAX 100001

using namespace std;

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

vector<int> G[NMAX], Gt[NMAX], CtC[NMAX];

int n, m, d[NMAX], k, nr;
bool viz[NMAX];

void citire()
{
    int a, b;
    fin >> n >> m;
    for(int i = 1; i <= m; ++i)
    {
        fin >> a >> b;
        G[a].push_back(b);
        Gt[b].push_back(a);
    }
}

void DFS(int nod)
{
    viz[nod] = 1;
    for(int i = 0; i < G[nod].size(); i++)
        if(!viz[G[nod][i]]) DFS(G[nod][i]);
    d[++k] = nod;
}

void DFS_T(int nod)
{
    viz[nod] = 0;
    CtC[nr].push_back(nod);
    for(int i = 0; i < Gt[nod].size(); i++)
        if(viz[Gt[nod][i]]) DFS_T(Gt[nod][i]);
}

int main()
{
    citire();
    for(int i = 1; i <= n; i++)
        if(!viz[i]) DFS(i);
    for(int i = n; i > 0; i--)
        if(viz[d[i]])
        {
            nr++;
            DFS_T(d[i]);
        }
    fout << nr << '\n';
    for(int i = 1; i <= nr; i++)
    {
        for(int j = 0; j < CtC[i].size(); j++)
            fout << CtC[i][j] << ' ';
        fout << '\n';
    }
    return 0;
}