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


using namespace std;

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

int n,m,nrcomp;
vector <int> lista[100001],lista2[100001],comp[100001];
stack <int> S;
int viz[100001];


void dfs1(int x)
{
    viz[x]=1;
    for(auto it:lista[x])
        if(!viz[it])
            dfs1(it);
    S.push(x);
}

void dfs2(int x)
{
    viz[x]=1;
    for(auto it:lista2[x])
        if(!viz[it])
            dfs2(it);
    comp[nrcomp].push_back(x);
}

int main()
{
    f>>n>>m;
    for(int i=1;i<=m;i++)
    {
        int x,y;
        f>>x>>y;
        lista[x].push_back(y);
        lista2[y].push_back(x);
    }
    for(int i=1;i<=n;i++)
        if(!viz[i])
            dfs1(i);
    for(int i=1;i<=n;i++)
        viz[i]=0;
    while(!S.empty())
    {
        int nod=S.top();
        if(!viz[nod])
        {
            nrcomp++;
            dfs2(nod);
        }
        S.pop();
    }
    g<<nrcomp;
    for(int i=1;i<=nrcomp;i++)
    {
        g<<'\n';
        for(auto it:comp[i])
            g<<it<<" ";
    }
    return 0;
}