#include <bits/stdc++.h>

using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
const int nmax = 100005;
int N,M,a[nmax],len,Lg;
bool viz[nmax];
vector < int > L[nmax];
vector < int > T[nmax];
vector < int > ans[nmax];


inline void Read()
{
    int x,y;
    fin >> N >> M;
    while(M--)
    {
        fin >> x >> y;
        L[x].push_back(y);
        T[y].push_back(x);
    }
}

inline void DFS1(int nod)
{
    viz[nod] = true;
    for(auto it : L[nod])
        if(!viz[it]) DFS1(it);
    a[++len] = nod;
}

inline void DFS2(int nod)
{
    viz[nod] = false;
    ans[Lg].push_back(nod);
    for(auto it : T[nod])
        if(viz[it])
            DFS2(it);
}

inline void Solve()
{
    int i;
    for(i = 1; i <= N; i++)
        if(!viz[i]) DFS1(i);
    for(i = N; i; i--)
        if(viz[a[i]])
        {
            ++Lg;
            DFS2(a[i]);
        }
    fout << Lg << "\n";
    for(i = 1; i <= Lg; i++)
    {
        for(auto it : ans[i])
            fout << it << " ";
        fout << "\n";
    }
}


int main()
{
    Read();
    Solve();
    fout.close();
    return 0;
}