#include <iostream>
#include <vector>
#include <stack>
#include <algorithm>
#include <fstream>

using namespace std;

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

const int NMAX = 100005;

int m, n;
vector<int> G[NMAX];
vector<int>v;
vector<vector<int> >sol;
stack<int>st;
int ids[NMAX];
int lowlink[NMAX];
bool onStack[NMAX];
int id = 0;

void read()
{
    fin >> n >> m;
    while (m--)
    {
        int a, b;
        fin >> a >> b;
        G[a].push_back(b);
    }
}

void init()
{
    for (int i = 1; i <= n; i++)
        ids[i] = -1;
}

void dfs(int u)
{
    st.push(u);
    ids[u] = lowlink[u] = ++id;
    onStack[u] = true;

    for (int v : G[u])
    {
        if (ids[v] == -1)
        {
            dfs(v);
            lowlink[u] = min(lowlink[u], lowlink[v]);
        }
        else if(onStack[v])
            lowlink[u] = min(lowlink[u], lowlink[v]);
    }

    if (lowlink[u] == ids[u])
    {
        v.clear();
        while (!st.empty())
        {
            int nod = st.top();
            v.push_back(nod);
            onStack[nod] = false;
            lowlink[nod] = lowlink[u];
            st.pop();
            if (nod == u) break;
        }
        sort(v.begin(), v.end());
        sol.push_back(v);
    }

}

void solve()
{
    for (int i = 1; i <= n; i++)
        if (ids[i] == -1)
            dfs(i);
    fout << sol.size() << '\n';
    for (int i = 0; i < sol.size(); i++)
    {
        for (int e : sol[i])
            fout << e << ' ';
        fout << '\n';
    }
}

int main()
{
    read();
    init();
    solve();
    return 0;
}