#include<fstream>
#include<vector>
#include<bitset>
#include<stack>
#include<set>
using namespace std;
#define NMAX 100005
ifstream fin("ctc.in");
ofstream fout("ctc.out");
vector <int> v[NMAX];
set <int> R[NMAX];
set <int>::iterator it;
stack <int> S;
bitset <NMAX> IS;
int n,m,g,k,D[NMAX],L[NMAX];
void dfs(int x)
{
    int i,y;
    S.push(x);
    IS[x]=1;
    L[x]=D[x]=++g;
    for (i=0;i<v[x].size();++i)
    {
        y=v[x][i];
        if (!D[y])
        {
            dfs(y);
            L[x]=min(L[x],L[y]);
        }
        else
            if (IS[y])
                L[x]=min(L[x],L[y]);
    }
    if (D[x]==L[x])
    {
        ++k;
        do
        {
            y=S.top();
            R[k].insert(y);
            S.pop();
            IS[y]=0;
        } while (y!=x);
    }
}
int main()
{
    int i,x,y;
    fin>>n>>m;
    for (i=0;i<m;++i)
    {
        fin>>x>>y;
        v[x].push_back(y);
    }
    for (i=1;i<=n;++i)
        if (!D[i])
            dfs(i);
    fout<<k<<"\n";
    for (i=1;i<=k;++i)
    {
        for (it=R[i].begin();it!=R[i].end();++it)
            fout<<*it<<" ";
        fout<<"\n";
    }
    return 0;
}