#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");

const int NMAX = 100001;

int viz1[NMAX], f[NMAX], k, n, m, nr, viz2[NMAX];

vector <int> g[NMAX];
vector <int> gt[NMAX];

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

void dfs1(int x)
{
    viz1[x] = 1;
    for(auto it : g[x])
    {
        if(!viz1[it])
        {
            dfs1(it);
        }
    }
    f[++k] = x;
}

void dfs2(int x)
{
    viz2[x] = 1;
    for(auto it : gt[x])
    {
        if(!viz2[it])
        {
            dfs2(it);
        }
    }
}

void dfs3(int x)
{
    fout << x << ' ';
    viz2[x] = 1;
    for(auto it : gt[x])
    {
        if(!viz2[it])
        {
            dfs3(it);
        }
    }
}

int main()
{
    citire();
    for(int i = 1; i <= n; i++)
    {
        if(!viz1[i])
            dfs1(i);
    }


    for(int i = k; i >= 1; i--)
    {
        if(!viz2[f[i]])
        {
            dfs2(f[i]);
            nr++;
        }
    }
    for(int i = 1; i <= n; i++)
    {
        viz2[i] = 0;
    }
    fout << nr << '\n';
    for(int i = k; i >= 1; i--)
    {
        if(!viz2[f[i]])
        {
            dfs3(f[i]);
            fout << '\n';
        }
    }

    return 0;
}