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