#include <bits/stdc++.h>
#define nMax 100005

using namespace std;

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

int n, m;
vector <int> L[nMax], T[nMax], sol[nMax];
int st[nMax], nc, k;
bool viz[nMax];

inline void Read()
{
    int i, x, y;
    fin >> n >> m;
    for(i = 1; i <= m; i++)
    {
        fin >> x >> y;
        L[x].push_back(y);
        T[y].push_back(x);
    }
}

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

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

inline void Solve()
{
    int i;
    for(i = 1; i <= n; i++)
        if(!viz[i])
            DFS1(i);
    while(k)
    {
        i = st[k--];
        if(viz[i])
        {
            nc++;
            DFS2(i);
        }
    }
}

inline void Write()
{
    int i;
    fout << nc << "\n";
    for(i = 1; i <= nc; i++)
    {
        for(auto it : sol[i])
            fout << it << " ";
        fout << "\n";
    }
}

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