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

using namespace std;

ifstream cin("ctc.in");
ofstream cout("ctc.out");

int n, m;
vector <int> v[100005], gt[100005], ctc[100005];
int visited[100002];
stack <int> s;
int nr = 0;

void read()
{
    cin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        cin >> x >> y;
        v[x].push_back(y);
        gt[y].push_back(x);
    }
}

void dfs1(int node)
{
    visited[node] = true;
    for (auto it:v[node]) {
        if (visited[it] == false)
            dfs1(it);
    }
    s.push(node);
}

void dfs2(int node)
{
    ctc[nr].push_back(node);
    visited[node] = 2;
    for (auto it:gt[node])
    {
        if (visited[it] == 1) {
            dfs2(it);
        }
    }
}

void solve()
{
    for (int i = 1; i <= n; i++) {
        if (visited[i] == false) {
            dfs1(i);
        }
    }

    while (!s.empty())
    {
        int node = s.top();
        if (visited[node] == 1) {
            dfs2(node);
            nr++;
        }
        s.pop();
    }

    cout << nr << endl;
    for (int i = 0; i < nr; i++)
    {
        for (auto it:ctc[i]) {
            cout << it << " ";
        }
        cout << endl;
    }
}

int main()
{
    read();
    solve();
    return 0;
}