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