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

using namespace std;

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

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

VVI G;
VVI ctc;
stack<int> stk;
VI vtemp;
VI tin, tout;
VB inStack;
int timer = 0;

int n, m;

void DFSTarjan(int x);

int main()
{
    fin >> n >> m;
    G = VVI(n + 1);
    tin = tout = VI(n + 1);
    inStack = VB(n + 1);

    int x, y;
    for (int i = 1; i <= m; ++i)
    {
        fin >> x >> y;
        G[x].emplace_back(y);
    }

    for (int i = 1; i <= n; ++i)
        if (!tin[i])
            DFSTarjan(i);

    fout << ctc.size() << '\n';

    for (auto i : ctc)
    {
        for (auto j : i)
            fout << j << ' ';

        fout << '\n';
    }
}

void DFSTarjan(int x)
{
    tin[x] = tout[x] = ++timer;
    inStack[x] = true;
    stk.emplace(x);


    for (auto& y : G[x])
        if (!tin[y])
        {
            DFSTarjan(y);
            tout[x] = min(tout[x], tout[y]);
        }
        else
            if (inStack[y])
                tout[x] = min(tout[y], tout[x]);




    if (tout[x] == tin[x])
    {
        int  y;
        vtemp.clear();
        while (true)
        {
            y = stk.top();
            stk.pop();
            vtemp.emplace_back(y);
            inStack[y] = false;
            if (tin[y] == tout[x])
                break;

        }

        ctc.emplace_back(vtemp);

    }



}