#include<fstream>
#include<vector>
#include<stack>
#include<algorithm>
using namespace std;
ifstream cin("ctc.in");
ofstream cout("ctc.out");
struct graf
{
    int val,ind;
};
graf v[100002];
vector<vector<int> >mu1,mu2;
stack<int>st;
int n,m,x,y,f[100002];
void DFS1(int nod)
{
    f[nod]=1;
    for(int i=0; i<mu1[nod].size(); i++)
        if(f[mu1[nod][i]]==0)
            DFS1(mu1[nod][i]);
    st.push(nod);
}
void DFS2(int nod,int val)
{
    v[nod].val=val;
    for(int i=0; i<mu2[nod].size(); i++)
        if(v[mu2[nod][i]].val==0)
            DFS2(mu2[nod][i],val);
}
bool sorta(graf a,graf b)
{
    if(a.val>b.val)
        return 0;
    if(a.val==b.val && a.ind>b.ind)
        return 0;
    return 1;
}
int main()
{
    cin>>n>>m;
    mu1.resize(n+1);
    mu2.resize(n+1);
    for(int i=1; i<=m; i++)
    {
        cin>>x>>y;
        mu1[x].push_back(y);
        mu2[y].push_back(x);
    }
    for(int i=1; i<=n; i++)
    {
        if(f[i]==0)
            DFS1(i);
        v[i].ind=i;
    }
    int cnt=1;
    while(st.empty()==0)
    {
        int q=st.top();
        st.pop();
        if(v[q].val==0)
        {
            DFS2(q,cnt);
            cnt++;
        }
    }
    sort(v+1,v+n+1,sorta);
    cout<<cnt-1<<'\n';
    cnt=1;
    for(int i=1; i<=n; i++)
    {
        if(v[i].val==cnt)
           cout<<v[i].ind<<' ';
        else
        {
            cout<<'\n';
            cnt++;
            cout<<v[i].ind<<' ';
        }
    }
}