#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#define nl '\n'

using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

const int NMAX = 100000;

int n, m, nrc;
vector<int> g[NMAX+1], ctc[NMAX+1];
int d[NMAX+1], dmin[NMAX+1], timp = 0;

stack<int> s;
bool inSt[NMAX+1];

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

void dfs(int x)
{
    d[x] = ++timp;
    dmin[x] = d[x];
    s.push(x);
    inSt[x] = 1;
    for (auto &y : g[x])
    {
        if (d[y] == 0)
        {
            dfs(y);
            dmin[x] = min(dmin[x], dmin[y]);
        }
        else
        {
            if (inSt[y] == 1)
                dmin[x] = min(dmin[x], d[y]);
        }
    }
    if (dmin[x] == d[x])
    {
        int u;
        nrc++;
        do
        {
            u = s.top();
            ctc[nrc].push_back(u);
            s.pop();
            inSt[u] = 0;
        }
        while (x != u);
    }
}

void afisare()
{
    fout << nrc << nl;
    for (int i = 1; i <= nrc; i++)
    {
        for (auto &x : ctc[i])
            fout << x << ' ';
        fout << nl;
    }
    return;
}

int main()
{
    citire();
    for (int i = 1; i <= n; i++)
    {
        if (d[i] == 0)
            dfs(i);
    }
    afisare();

    return 0;
}