#include <fstream>
#include<stack>
#include<list>

using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
int pe_stiva[100003],n,m,x,y,idx[100003],lowlink[100003],nrcomp,index;

stack<int>s;
list<int>v[100002];
list<int>comp[100002];

void tarjan(int k)
{
    int u;
    list<int>::iterator it;
    idx[k]=index;
    lowlink[k]=index;
    index++;
    s.push(k); pe_stiva[k]=1;
    for(it=v[k].begin();it!=v[k].end();++it)
    {
        u=*it;
        if(idx[u]==0)
        {
            tarjan(u);
            lowlink[k]=min(lowlink[k],lowlink[u]);
        }
        else if(pe_stiva[u])
            lowlink[k]=min(lowlink[k],idx[u]);
    }
    if(lowlink[k]==idx[k])
    {
        nrcomp++;
        u=s.top();
        do{
            u=s.top();
            comp[nrcomp].push_back(u);
            s.pop();
            pe_stiva[u]=0;
        }while(u!=k);
    }
}

int main()
{
    int i;
    index=1;
    f>>n>>m;
    for(i=1;i<=m;i++)
    {
        f>>x>>y;
        v[x].push_back(y);
    }
    for(i=1;i<=n;i++)
        if(idx[i]==0) tarjan(i);
    list<int>::iterator it1;
    g<<nrcomp<<'\n';
    for(i=1;i<=nrcomp;i++)
    {
        for(it1=comp[i].begin();it1!=comp[i].end();it1++) g<<*it1<<' ';
        g<<'\n';
    }
    f.close();
    g.close();
    return 0;
}