#include <bits/stdc++.h>

using namespace std;

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

int n, m;
int componente;
int cnt;
vector<int>V[100005];
vector<int>T[100005];
vector<int>CTC[100005];
int viz[100005];
int a[100005];
void Citire()
{
    fin >> n >> m;
    for(int i = 1;i <= m;i++)
    {
        int x, y;
        fin >> x >> y;
        V[x].push_back(y);
        T[y].push_back(x);
    }
}
void DFS1(int nod)
{
    viz[nod] = 1;
    for(auto x : V[nod])
        if(viz[x] == 0)
            DFS1(x);
    a[++cnt] = nod;
}

void DFS2(int nod)
{
    viz[nod] = 0;
    CTC[componente].push_back(nod);
    for(auto x : T[nod])
        if(viz[x] == 1)
            DFS2(x);
}
int main()
{
    int i;
    Citire();
    for(i = 1;i <= n;i++)
        if(viz[i] == 0)
            DFS1(i);
    for(i = cnt;i >= 1;i--)
        if(viz[a[i]] == 1)
        {
            componente++;
            DFS2(a[i]);
        }
    fout << componente << "\n";
    for(i = 1;i <= componente;i++, fout << "\n")
        for(auto x : CTC[i])
            fout << x << " ";
    return 0;
}