#include <bits/stdc++.h>

using namespace std;
vector<int>graph[100005], graph_inversat[100005], topo_sort;
vector<vector<int>> componente_conexe;
bool viz[100005];
void dfs(int nod)
{
    viz[nod]=1;
    for(auto x:graph[nod])
    {
        if(!viz[x])
            dfs(x);
    }
    topo_sort.push_back(nod);
}
void ctc(int nod)
{
    viz[nod]=0;
    for(auto x: graph_inversat[nod])
    {
        if(viz[x])
            ctc(x);
    }
    componente_conexe.back().push_back(nod);
}
int main()
{
    ifstream cin("ctc.in");
    ofstream cout("ctc.out");
    int n,m;
    cin>>n>>m;
    for(int i=1; i<=m; i++)
    {
        int a,b;
        cin>>a>>b;
        graph[a].push_back(b);
        graph_inversat[b].push_back(a);
    }
    for(int i=1; i<=n; i++)
    {
        if(!viz[i])
            dfs(i);
    }
    reverse(topo_sort.begin(), topo_sort.end());
    for(auto x:topo_sort)
    {
        if(viz[x])
        {
            componente_conexe.push_back(vector<int>());
            ctc(x);
        }
    }
    cout<<componente_conexe.size()<<'\n';
    for(auto componenta: componente_conexe)
    {
        for(auto x: componenta)
            cout<<x<<" ";
        cout<<'\n';
    }
    return 0;
}