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

using namespace std;

const int NMAX = 100000 + 5;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

vector <int> ans[NMAX];
vector <int> graph[NMAX], hparg[NMAX];
stack <int> s;
int n, m, ctc;
bool vis[NMAX];

void dfs(int node)
{
    vis[node] = true;
    for (int i: graph[node])
        if (!vis[node])
            dfs(i);
    s.push(node);
}

void sfd(int node)
{
    vis[node] = true;
    ans[ctc].push_back(node);
    for (int i: graph[node])
        if (!vis[i])
            sfd(i);
}

void write()
{
    fout << ctc << '\n';
    for (int i = 1; i <= ctc; ++i)
    {
        for (int j: ans[ctc])
            fout << j << " ";
        fout << '\n';
    }
}

void read()
{
    int x, y;

    fin >> n >> m;
    for (int i = 1; i <= m; ++i)
    {
        fin >> x >> y;
        graph[x].push_back(y);
        hparg[y].push_back(x);
    }
}

int main()
{
    read();
    for (int i = 1; i <= n; ++i)
        if (!vis[i])
            dfs(i);
    memset(vis, 0, sizeof(vis));
    while (!s.empty())
    {
        int x = s.top();
        s.pop();
        if (!vis[x])
        {
            ++ctc;
            sfd(x);
        }
    }
    write();

    return 0;
}