#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
vector <vector<int>> S;
vector <int> v[100011];
stack <int> q;
bool instk[100011];
void tareconex(int k)
{
    int nod;
    vector <int> s;
    while(nod!=k)
    {
        nod=q.top();
        q.pop();
        s.push_back(nod);
        instk[nod]=0;
    }
    S.push_back(s);
}
int when[100011],low[100011],index;
void tarjan(int k)
{
    index++;
    when[k]=low[k]=index;
    q.push(k);
    instk[k]=1;
    for(int i=0;i<v[k].size();i++)
        if(when[v[k][i]]==0)
        {
            tarjan(v[k][i]);
            low[k]=min(low[k],low[v[k][i]]);
        }
        else
        if(instk[v[k][i]]==1)
            low[k]=min(low[k],low[v[k][i]]);
    if(when[k]==low[k])
        tareconex(k);
}
int n,m,x,y,i,j;
int main()
{
    f>>n>>m;
    for(i=1;i<=m;i++)
    {
        f>>x>>y;
        v[x].push_back(y);
    }
    index=0;
    for(i=1;i<=n;i++)
        if(when[i]==0)
            tarjan(i);
    g<<S.size()<<'\n';
    for(i=0;i<S.size();i++,g<<'\n')
        for(j=0;j<S[i].size();j++)
        g<<S[i][j]<<" ";
    return 0;
}