#include<fstream>
#include<vector>
#include<stack>
using namespace std;
vector<int> v[100005],ctc[100005];
stack<int>st;
int low[100005],lev[100005],nr,id=1;
bool viz[100005];
void tarjan(int dad)
{
    int i,son,nod;
    low[dad]=lev[dad]=id++;
    viz[dad]=true;
    st.push(dad);
    for(i=0;i<v[dad].size();i++)
    {
        son=v[dad][i];
        if(lev[son]==0)
        {
            tarjan(son);
            low[dad]=min(low[dad], low[son]);
        }
        else if(viz[son]==true)
            low[dad]=min(low[dad], low[son]);
    }
    if(low[dad]==lev[dad])
    {
        nr++;
        do{
            nod=st.top();
            st.pop();
            ctc[nr].push_back(nod);
            viz[nod]=false;
        }while(nod!=dad);
    }
}
int main()
{
    ifstream f("ctc.in");
    ofstream g("ctc.out");
    int n,m,x,y,i,j;
    f>>n>>m;
    for(i=1;i<=m;i++)
    {
        f>>x>>y;
        v[x].push_back(y);
    }
    for(i=1;i<=n;i++)
      if(lev[i]==0)
        tarjan(i);
    g<<nr<<"\n";
    for(i=1;i<=nr;i++)
    {
        for(j=0;j<ctc[i].size();j++)
          g<<ctc[i][j]<<" ";
        g<<"\n";
    }
    return 0;
}