#include <iostream>
#include <vector>
#include <fstream>
#include <deque>
#include <bitset>
#define dim 100005
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
bitset<dim> iq;
deque<int> q;
vector <int> L[dim],aux;
vector< vector<int> > sol;
int low[dim],niv[dim],g,n,m,i,x,y;
void dfs(int nod)
{
    iq[nod]=1;
    niv[nod]=++g;
    low[nod]=g;
    q.push_back(nod);
    for(auto it:L[nod])
    {
        if(niv[it]==0)
        {
            dfs(it);
            low[nod]=min(low[nod],low[it]);
        }
        else if(iq[it]==1)
        {
            low[nod]=min(low[nod],low[it]);

        }
    }
    if(low[nod]==niv[nod])
    {
        aux.clear();
        int x=0;
        while(x!=nod)
        {
            x=q.back();
            iq[x]=0;
            q.pop_back();
            aux.push_back(x);
        }
        sol.push_back(aux);
    }
}
int main()
{
    fin>>n>>m;
    for(i=1; i<=m; i++)
    {
        fin>>x>>y;
        L[x].push_back(y);
    }
    for(i=1; i<=n; i++)
    {
        if(niv[i]==0)
        {
            dfs(i);
        }
    }
    fout<<sol.size()<<"\n";
    for(auto &vec:sol)
    {
        for(auto &it:vec)
            fout<<it<<" ";
        fout<<"\n";
    }
}