#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");
int n,m,a1,b1,ap[100005],ind,indice[100005],t;
bool b[100005];
vector <int> v[100005];
vector <int>sol1[100005];
stack <int> s;
void sol(int nod)
{
    indice[nod]=++ind;
    ap[nod]=ind;
    s.push(nod);
    for(auto i:v[nod])
    {
        if(ap[i]==0)
        {
            sol(i);
            ap[nod]=min(ap[nod],ap[i]);
        }
        else
        {
            ap[nod]=min(ap[nod],ap[i]);
        }
    }
    if(ap[nod]==indice[nod])
    {
        t++;
        while(s.top()!=nod)
        {
            sol1[t].push_back(s.top());
            s.pop();
        }
        sol1[t].push_back(s.top());
        s.pop();
    }
}
int main()
{
    in>>n>>m;
    for(int i=1;i<=m;i++)
    {
        in>>a1>>b1;
        v[a1].push_back(b1);
    }
    for(int i=1;i<=n;i++)
    {
        if(ap[i]==0)
        {
            sol(i);
        }
    }
    out<<t<<'\n';
    for(int i=1;i<=t;i++)
    {
        for(auto j:sol1[i])out<<j<<' ';
        out<<'\n';
    }
    return 0;
}