#include <bits/stdc++.h>

using namespace std;

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

vector<int>v[100003];
vector<int>comp[100003];
stack<int>s;
int index,idx[100003],lowlink[100003],n,m,nrcomp;
bool pe_stiva[100003];

void tarjan(int k)
{
    int u;
    s.push(k);
    pe_stiva[k]=1;

    idx[k]=index;
    lowlink[k]=index;
    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]);
        }
    }
    int x;
    if(lowlink[k]==idx[k])
    {
        ++nrcomp;
        do{
            x=s.top();
            pe_stiva[x]=0;
            comp[nrcomp].push_back(x);
            s.pop();
        }while(x!=k);
        //g<<'\n';
    }
}

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