#include <fstream>
#include <vector>

using namespace std;

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

int n,m;
vector <int> graph[100002],grapht[100002],sol[100002];
int v[100002],ss;
bool viz[100002];

void dfs(int nod)
{
    viz[nod]=1;
    for(int i=0;i<grapht[nod].size();++i)
        if(!viz[grapht[nod][i]])
            dfs(grapht[nod][i]);
    sol[ss].push_back(nod);
}
void sortaret(int nod)
{
    viz[nod]=1;
    for(int i=0;i<graph[nod].size();++i)
        if(!viz[graph[nod][i]])
            sortaret(graph[nod][i]);
    v[++v[0]]=nod;
}
int main()
{
    f>>n>>m;
    int x,y;
    for(int i=1;i<=m;++i)
    {
        f>>x>>y;
        graph[x].push_back(y);
        grapht[y].push_back(x);
    }
    for(int i=1;i<=n;++i)
        if(!viz[i])
            sortaret(i);
    for(int i=1;i<=n;++i)
        viz[i]=0;
    for(int i=v[0];i>=1;--i)
        if(!viz[v[i]])
            ++ss,dfs(v[i]);
    g<<ss<<"\n";
    for(int i=1;i<=ss;++i,g<<"\n")
        for(int j=0;j<sol[i].size();++j)
            g<<sol[i][j]<<" ";

    return 0;
}