#include <fstream>
#include<vector>
#include<stack>
#include<bitset>

using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");

int idx[100003],lowlink[100003],n,m,index,nrcomp;

bitset<100003>pe_stiva;
vector<int>v[100003];
vector<int>comp[100003];
stack<int>s;

void tarjan(int k)
{
    int u;
    idx[k]=index;
    lowlink[k]=index;
    s.push(k);
    pe_stiva[k]=1;
    index++;
    vector<int>::iterator it;
    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++;
        do
        {
            u=s.top();
            s.pop();
            pe_stiva[u]=0;
            comp[nrcomp].push_back(u);
        }while(u!=k);
    }
}

int main()
{
    int x,y,i;
    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);
    vector<int>::iterator it;
    g<<nrcomp<<'\n';
    for(i=1;i<=nrcomp;i++)
    {
        for(it=comp[i].begin();it!=comp[i].end();++it)
            g<<*it<<' ';
        g<<'\n';
    }
    f.close();
    g.close();
    return 0;
}