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

using namespace std;

const int N = 1e5 + 5;

vector <int> L[N], T[N], scc[N];
int n, nr_scc;

void Read ()
{
    ifstream fin ("ctc.in");
    int m;
    fin >> n >> m;
    while (m--)
    {
        int x, y;
        fin >> x >> y;
        L[x].push_back(y);
        T[y].push_back(x);
    }
    fin.close();
}

stack <int> st;
bitset <N> seen;

void DFS1(int vertex)
{
    seen[vertex] = 1;
    for (auto next : L[vertex])
        if (!seen[next])
            DFS1(next);
    st.push(vertex);
}

void DFS2(int vertex)
{
    seen[vertex] = 0;
    for (auto next : T[vertex])
        if (seen[next])
            DFS2(next);
    scc[nr_scc].push_back(vertex);
}

void Kosaraju ()
{
    for (int i = 1; i <= n; i++)
        if (!seen[i])
            DFS1(i);
    while (!st.empty())
    {
        if (seen[st.top()])
        {
            nr_scc++;
            DFS2(st.top());
        }
        st.pop();
    }
    ofstream fout ("ctc.out");
    fout << nr_scc << "\n";
    for (int i = 1; i <= nr_scc; i++)
    {
        for (auto j : scc[i])
            fout << j << " ";
        fout << "\n";
    }
    fout.close();
}

int main()
{
    Read();
    Kosaraju();
    return 0;
}