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

using VI = vector<int>;
using VVI = vector<VI>;
using VB = vector<bool>;

int n, m, nv;
VVI G, ctc;
VI niv, L, c;
stack<int> stk;
VB inStack;

void Read();
void Df(int x);
void Write();

int main()
{
    Read();
    for (int x = 1; x <= n; x++)
        if (!niv[x])
            Df(x);
    Write();
}

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

void Df(int x)
{
    niv[x] = L[x] = ++nv;
    stk.push(x), inStack[x] = true;
    for (const int& y : G[x])
        if (!niv[y])
        {
            Df(y);
            L[x] = min(L[x], L[y]);
        }
        else
            if (inStack[y])
                L[x] = min(L[x], niv[y]);
    if (L[x] == niv[x])
    {
        c.clear();
        while (!stk.empty())
        {
            int top = stk.top();
            stk.pop();
            inStack[top] = false;
            c.push_back(top);
            if (top == x)
                break;
        }
        ctc.push_back(c);
    }
}

void Read()
{
    ifstream fin("ctc.in");
    fin >> n >> m;
    G = VVI(n + 1);
    niv = L = VI(n + 1);
    inStack = VB(n + 1);
    int x, y;
    while (m--)
    {
        fin >> x >> y;
        G[x].push_back(y);
    }
    fin.close();
}