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

using namespace std;

vector <int> L[Nmax], T[Nmax], sol[Nmax];
int n, m, st[Nmax], ncc, top;
bitset <Nmax> viz;

void Citire()
{
    ifstream f("ctc.in");
    f >> n >> m;
    int i, x, y;
    for(i = 1; i <= m; i++)
    {
        f >> x >> y;
        L[x].push_back(y);
        T[y].push_back(x);
    }
    f.close();
}

void DFS1(int nod)
{
    viz[nod] = 1;
    for(auto nnod : L[nod])
        if(!viz[nnod])
            DFS1(nnod);
    st[++top] = nod;
}

void DFS2(int nod)
{
    viz[nod] = 0;
    for(auto nnod : T[nod])
        if(viz[nnod])
            DFS2(nnod);
    sol[ncc].push_back(nod);
}

void Rezolvare()
{
    int i;
    for(i = 1; i <= n; i++)
        if(viz[i] == 0)
            DFS1(i);
    while(top > 0)
    {
        i = st[top--];
        if(viz[i] == 1)
        {
            ncc++;
            DFS2(i);
        }
    }
}

void Afisare()
{
    ofstream g("ctc.out");
    g << ncc << "\n";
    for(int i = 1; i <= ncc; i++)
    {
        for(auto j : sol[i])
            g << j << " ";
        g << "\n";
    }
}

int main()
{
    Citire();
    Rezolvare();
    Afisare();
    return 0;
}