#include <bits/stdc++.h>

using namespace std;

const int N_MAX = 100002;

int n, m;

vector <int> outEdges[N_MAX];
vector <int> inEdges[N_MAX];

int order[N_MAX];
int currentIndex;

bool visited[N_MAX];

void dfs (int u)
{
    visited[u] = true;
    for(int v : outEdges[u])
        if(visited[v] == false)
            dfs(v);
    order[u] = ++currentIndex;
}

int cntSCC;
vector <int> SCC[N_MAX];

void dfsSCC (int u)
{
    visited[u] = true;
    SCC[cntSCC].push_back(u);
    for(int v : inEdges[u])
        if(visited[v] == false)
            dfsSCC(v);
}


int main()
{
    ifstream fin ("ctc.in");
    ofstream fout ("ctc.out");
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int u, v;
        fin >> u >> v;
        outEdges[u].push_back(v);
        inEdges[v].push_back(u);
    }
    for(int i = 1; i <= n; i++)
        if(visited[i] == false)
            dfs(i);
    memset(visited, false, sizeof(visited));
    for(int i = n; i >= 1; i--)
        if(visited[order[i]] == false)
        {
            cntSCC++;
            dfsSCC(order[i]);
        }
    fout << cntSCC << "\n";
    for(int i = 1; i <= cntSCC; i++, fout << "\n")
        for(int u : SCC[i])
            fout << u << " ";
    return 0;
}