#include <fstream>
#include <vector>
#include <stack>
using namespace std;

int n, m;
vector<vector<int>> G, Gt;
vector<bool> visited;
stack<int> stk;
vector<int> cc;
vector<vector<int>> ctc;

void Read();
void Dfs1(int x);
void Dfs2(int x);
void Write();

int main()
{
    Read();
    for (int x = 1; x <= n; x++)
        if (!visited[x])
            Dfs1(x);
    
    visited = vector<bool>(n + 1);
    int x;
    while (!stk.empty())
    {
        x = stk.top();
        stk.pop();
        if (!visited[x])
        {
            cc = vector<int>();
            Dfs2(x);
            ctc.emplace_back(cc);
        }
    }
    
    Write();
}

void Dfs2(int x)
{
    visited[x] = true;
    cc.emplace_back(x);
    for (const int& y : G[x])
        if (!visited[y])
            Dfs2(y);
}

void Dfs1(int x)
{
    visited[x] = true;
    for (const int& y : Gt[x])
        if (!visited[y])
            Dfs1(y);
    stk.emplace(x);
}

void Write()
{
    ofstream fout("ctc.out");
    fout << ctc.size() << '\n';
    for (const auto& c : ctc)
    {
        for (const int& x : c)
            fout << x << ' ';
        fout << '\n';
    }
}

void Read()
{
    ifstream fin("ctc.in");
    fin >> n >> m;
    G = Gt = vector<vector<int>>(n + 1);
    visited = vector<bool>(n + 1);
    
    int x, y;
    while (m--)
    {
        fin >> x >> y;
        G[x].emplace_back(y);
        Gt[y].emplace_back(x);
    }
}