#include <iostream>
#include <vector>
#include <stdlib.h>

#define IOS ios :: sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define NMAX 100005

using namespace std;

vector <int> muchii1[NMAX], muchii2[NMAX], H;
int n, m;
bool viz[NMAX];

vector <vector <int> > ans;

void DFS1(int nod)
{
    viz[nod] = 1;
    for (auto it : muchii1[nod])
    {
        if (viz[it])
            continue;
        DFS1(it);
    }
    H.push_back(nod);
}

void DFS2(int nod)
{
    viz[nod] = 1;
    for (auto it : muchii2[nod])
    {
        if (viz[it])
            continue;
        DFS2(it);
    }
    ans.back().push_back(nod);
}

int main()
{
    cin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        cin >> x >> y;
        muchii1[x].push_back(y);
        muchii2[y].push_back(x);
    }
    for (int i = 1; i <= n; i++)
        if (!viz[i])
            DFS1(i);
    memset(viz, 0, sizeof(viz));
    for (int i = H.size() - 1; i >= 0; i--)
        if (!viz[H[i]])
        {
            ans.push_back(vector <int>());
            DFS2(H[i]);
        }
    cout << ans.size() << '\n';
    for (int i = 0; i < ans.size(); i++)
    {
        for (int j = 0; j < ans[i].size(); j++)
            cout << ans[i][j] << ' ';
        cout << endl;
    }
    return 0;
}