#include<fstream>
#include<vector>
#include<stack>
#include<bitset>
using namespace std;
#define NMAX 100005
ifstream fin("ctc.in");
ofstream fout("ctc.out");
vector <int> v[NMAX],R[NMAX];
stack <int> st;
bitset <NMAX> IS;
int n,m,k,x,y,g,Niv[NMAX],Low[NMAX];
void dfs(int s)
{
    int i,z;
    Niv[s]=Low[s]=++g;
    st.push(s);
    IS[s]=1;
    for (i=0;i<v[s].size();++i)
    {
        z=v[s][i];
        if (!Niv[z])
        {
            dfs(z);
            Low[s]=min(Low[s],Low[z]);
        }
        else
            if (IS[z])
                Low[s]=min(Low[s],Low[z]);

    }
    if (Niv[s]==Low[s])
    {
        ++k;
        do
        {
            z=st.top(); st.pop();
            IS[z]=0;
            R[k].push_back(z);
        } while (z!=s);
    }
}
int main()
{
    int i,j;
    fin>>n>>m;
    for (i=0;i<m;++i)
    {
        fin>>x>>y;
        v[x].push_back(y);
    }
    for (i=1;i<=n;++i)
        if (!Niv[i])
            dfs(i);
    fout<<k<<"\n";
    for (i=1;i<=k;++i)
    {
        for (j=0;j<R[i].size();++j)
            fout<<R[i][j]<<" ";
        fout<<"\n";
    }
    return 0;
}