#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <stack>

using namespace std;

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

int n, m, id, scc;
int low[100001], ids[100001];
bool onStack[100001];
vector <int> V[100001];
vector <int> vec[100001];
stack <int> S;

void DFS(int at)
{
    S.push(at);
    onStack[at] = true;
    ids[at] = low[at] = id++;

    for (int i = 0; i < V[at].size(); i++)
    {
        int to = V[at][i];
        if (ids[to] == 0)
        {
            DFS(to);
        }
        if (onStack[to] == true)
        {
            low[at] = min(low[at], low[to]);
        }
    }

    if (ids[at] == low[at])
    {
        scc++;
        while (S.empty() == false)
        {
            int node = S.top();
            S.pop();
            onStack[node] = false;
            vec[scc].push_back(node);
            if (node == at)
            {
                break;
            }
        }
    }
}

int main()
{
    f >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        f >> x >> y;
        V[x].push_back(y);
    }

    for (int i = 1; i <= n; i++)
    {
        if (ids[i] == 0)
        {
            DFS(i);
        }
    }

    g << scc << endl;
    for (int i = 1; i <= scc; i++)
    {
        sort(vec[i].begin(), vec[i].end());
        for (int j = 0; j < vec[i].size(); j++)
        {
            g << vec[i][j] << " ";
        }
        g << endl;
    }
}