#include <bits/stdc++.h>
#define nmax 100001
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
int n,m,timp[nmax],k,nr;
vector<int>L[nmax];
vector<int>Z[nmax];
bitset<nmax>viz;
vector<int>solutie[nmax];
void Read()
{
    int i,x,y;
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        L[x].push_back(y);
        Z[y].push_back(x);
    }
}
void DFS_First(int varf)
{
    int i,x;
    viz[varf]=1;
    for(i=0;i<L[varf].size();i++)
    {
        x=L[varf][i];
        if(!viz[x])
            DFS_First(x);
    }
    timp[++k]=varf;
}
void DFS_Second(int varf)
{
    int i,x;
    viz[varf]=1;
    for(i=0;i<Z[varf].size();i++)
    {
        x=Z[varf][i];
        if(!viz[x])
            DFS_Second(x);
    }
    solutie[nr].push_back(varf);
}
void Solve()
{
    int i,j;
    for(i=1;i<=n;i++)
        if(!viz[i])
            DFS_First(i);
    viz.reset();
    for(i=k;i>=1;i--)
    {
        if(!viz[timp[i]])
        {
            nr++;
            DFS_Second(timp[i]);
        }
    }
    fout<<nr<<"\n";
    for(i=1;i<=nr;i++)
    {
        sort(solutie[i].begin(),solutie[i].end());
        for(j=0;j<solutie[i].size();j++)
            fout<<solutie[i][j]<<" ";
        fout<<"\n";
    }
}
int main()
{
    Read();
    Solve();
    fin.close();
    fout.close();
    return 0;
}