#include <fstream>
#include <vector>
#include <stack>
using namespace std;

ifstream cin("ctc.in");
ofstream cout("ctc.out");
vector <int> G[100001],rez[100001],GT[100001];
int viz[100001],n,m,ctc;
stack <int> s;
void DFS(int start)
{
    viz[start]=1;
    for(unsigned int i=0; i<G[start].size(); ++i)
        if(!viz[G[start][i]])
            DFS(G[start][i]);
    s.push(start);
}
void DFS_T(int start)
{
    viz[start]=2;
    rez[ctc].push_back(start);
    for(unsigned int i=0; i<GT[start].size(); ++i)
        if(viz[GT[start][i]]==1)
            DFS_T(GT[start][i]);
}
int main()
{
    cin>>n>>m;
    while(m--)
    {
        int x,y;
        cin>>x>>y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
    for(int i=1;i<=n;++i)
        if(!viz[i])
            DFS(i);
    while(!s.empty())
    {
        int v = s.top();
        if(viz[v]==1)
        {
            ctc++;
            DFS_T(v);
        }
        s.pop();
    }
    cout<<ctc<<'\n';
    for(int i=1;i<=ctc;++i,cout<<'\n')
    {
        for(auto it:rez[i])
            cout<<it<<' ';
    }
    return 0;
}