#include <bits/stdc++.h>
#define nmax 100005
#define ull unsigned long long

using namespace std;

ifstream f("ctc.in");
ofstream g("ctc.out");

int n, m, nrc;
int viz[nmax];
vector <int> a[nmax], atr[nmax];
vector <int> sol[nmax];
stack <int> s;

void Read()
{
    f >> n >> m;

    for(int i = 0; i < m; i++)
    {
        int x, y;

        f >> x >> y;
        a[x].push_back(y);
        atr[y].push_back(x);
    }
}

void dfs(int nod)
{
    viz[nod] = 1;

    for(unsigned int i = 0; i < a[nod].size(); i++)
    {
        if(!viz[a[nod][i]])
            dfs(a[nod][i]);
    }
    s.push(nod);
}

void dfs2(int nod)
{
    viz[nod] = 2;
    sol[nrc].push_back(nod);

    for(unsigned int i = 0; i < atr[nod].size(); i++)
    {
        if(viz[atr[nod][i]] == 1)
            dfs2(atr[nod][i]);
    }

}

void Solve()
{
    for(int i = 1; i <= n; i++)
    {
        if(!viz[i])
            dfs(i);
    }

    while(!s.empty())
    {
        int nod = s.top();
        //cout << nod << ' ';

        if(viz[nod] == 1)
        {
            nrc++;
            dfs2(nod);
        }
        s.pop();
    }
}

void Afis()
{
    g << nrc << '\n';
    for(int i = 1; i <= nrc; i++)
    {
        for(unsigned int j = 0; j < sol[i].size(); j++)
            g << sol[i][j] << ' ';
        g << '\n';
    }
}

int main()
{
    Read();
    Solve();
    Afis();
}