#include <bits/stdc++.h>
#define nmax 100001
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
int viz[nmax],vizt[nmax],timp[nmax],n,m,k,sol;
vector<int>h[nmax];
vector<int>b[nmax];
vector<int>c[nmax];
void Citire()
{
    int i,x,y;
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        h[x].push_back(y);
        c[y].push_back(x);
    }
}
inline void DFS_Timp(int x)
{
    int i;
    viz[x]=1;
    for(i=0;i<h[x].size();i++)
        if(!viz[h[x][i]])
            DFS_Timp(h[x][i]);
    timp[++k]=x;
}
inline void DFS_Rezolvare(int x)
{
   int i;
    vizt[x]=1;
    for(i=0;i<c[x].size();i++)
        if(!vizt[c[x][i]])
            DFS_Rezolvare(c[x][i]);
    b[sol].push_back(x);
}
int main()
{
    int i,j;
    Citire();
    for(i=n;i>=1;i--)
        if(!viz[i])
            DFS_Timp(i);
    for(i=k;i>=1;i--)
    {
        if(!vizt[timp[i]])
        {
            sol++;
            DFS_Rezolvare(timp[i]);
        }
    }
    fout<<sol<<"\n";
    for(i=1;i<=sol;i++)
    {
        sort(b[i].begin(),b[i].end());
        for(j=0;j<b[i].size();j++)
            fout<<b[i][j]<<" ";
        fout<<"\n";
    }
    fin.close();
    fout.close();
    return 0;
}