#include<iostream>
#include <bits/stdc++.h>
using namespace std;

vector<int> a[100003];
vector<int> b[100003];
vector<int> ctc[100003];
int n, m, nrc;
int st[100003], top;
int viz[100003];
ifstream f("ctc.in");
ofstream g("ctc.out");

void read()
{
    int i, j;
    f >> n >> m;
    for (int k = 1; k <= m; k++)
    {
        f >> i >> j;
        a[i].push_back(j);
        b[j].push_back(i);
    }
}

void DFSTop(int k)
{
    viz[k] = 1;
    for (int i : a[k])
        if (viz[i] == 0) DFSTop(i);
    st[++top] = k;
}

void DFS(int k)
{
    viz[k] = 0;
    for (int i : b[k])
        if (viz[i] == 1) DFS(i);
    ctc[nrc].push_back(k);
}

void CTC()
{
    int i;
    for (i = 1; i <= n; i++)
        if (viz[i] == 0)
            DFSTop(i);
    for (i = n; i >= 1; i--)
        if (viz[st[i]] == 1)
        {
            nrc++;
            DFS(st[i]);
        }
}

void show()
{
    g << nrc << "\n";
    for (int i = 1; i <= nrc; i++)
    {
        for (int j : ctc[i])
            g << j << " ";
        g << "\n";
    }
}

int main()
{
    read();
    CTC();
    show();
    f.close();
    g.close();
    return 0;
}