#include <bits/stdc++.h>
#define newline '\n'
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
///***********************
const int NMAX = 1e5 + 3;
int n, m, nrSCCs;
array<vector<int>, NMAX> graph, tranGraph, SCC;
array<int, NMAX> nrVis;
stack<int> st;

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

void dfs(int start)
{
    nrVis[start] = 1;
    for (auto nei : graph[start])
        if (!nrVis[nei])
            dfs(nei);
    st.push(start);
}

void dfsTran(int start)
{
    nrVis[start] = 2;
    SCC[nrSCCs].push_back(start);

    for (auto nei : tranGraph[start])
        if (nrVis[nei] == 1)
            dfsTran(nei);
}

void solve()
{
    for (int i = 1; i <= n; i++)
        if (!nrVis[i])
            dfs(i);

    while (!st.empty())
    {
        if (nrVis[st.top()] == 1)
        {
            nrSCCs++;
            dfsTran(st.top());
        }
        st.pop();
    }
}

void display()
{
    fout << nrSCCs << newline;
    for (int i = 1; i <= nrSCCs; i++)
    {
        for (auto node : SCC[i])
            fout << node << ' ';
        fout << newline;
    }
}

int main()
{
    read();
    solve();
    display();
    fout.close();
    return 0;
}