#include <bits/stdc++.h>
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
const int NMAX=100005;
int n,m,tmp[NMAX],k,nrcmp;
vector<int>L[NMAX];
vector<int>Q[NMAX];
vector<int>SOL[NMAX];
bitset<NMAX>viz;
inline void READ()
{
    int nd,nd1;
    fin>>n>>m;
    while(m--)
    {
        fin>>nd>>nd1;
        L[nd].push_back(nd1);
        Q[nd1].push_back(nd);
    }
}
void DFS_FIRST(int varf)
{
    viz[varf]=1;
    for(auto i:L[varf])
        if(!viz[i])
            DFS_FIRST(i);
    ++k;
    tmp[k]=varf;
}
void DFS_SECOND(int varf)
{
    viz[varf]=1;
    for(auto i:Q[varf])
        if(!viz[i])
            DFS_SECOND(i);
    SOL[nrcmp].push_back(varf);
}
inline void SOLVE()
{
    for(int i=1;i<=n;i++)
        if(!viz[i])
            DFS_FIRST(i);
    viz.reset();
    for(int i=k;i>=1;i--)
    {
        int j=tmp[i];
        if(!viz[j])
        {
            nrcmp++;
            DFS_SECOND(j);
        }
    }
    fout<<nrcmp<<"\n";
    for(int i=1;i<=nrcmp;i++)
    {
        int lug=SOL[i].size();
        for(int j=0;j<lug;j++)
            fout<<SOL[i][j]<<" ";
        fout<<"\n";
    }

}
int main()
{
    READ();
    SOLVE();
    fin.close();
    fout.close();
    return 0;
}