#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream cin("ctc.in");
ofstream cout("ctc.out");

vector<vector<int> > sirad, cc;
vector<int> c, index, low;
vector<bool> viz, instk;
stack<int> st;
int n, m, idx;

void Tarjan();
void Dfs(int x);

int main()
{
    int a, b;
    cin >> n >> m;
    sirad = vector<vector<int>>(n + 1);
    index = low = vector<int>(n + 1);
    viz = instk = vector<bool>(n + 1);

    for (int i = 1; i <= m; ++i)
    {
        cin >> a >> b;
        sirad[a].push_back(b);
    }

    Tarjan();
    return 0;
}

void Tarjan()
{
    for (int i = 1; i <= n; ++i)
        if (!viz[i])
            Dfs(i);

    cout << cc.size() << '\n';
    for (auto i : cc)
    {
        for (auto j : i)cout << j << ' ';
        cout << '\n';
    }
}

void Dfs(int x)
{
    st.push(x);
    instk[x] = viz[x] = true;
    index[x] = low[x] = ++idx;

    for (auto i : sirad[x])
        if (!viz[i])
        {
            Dfs(i);
            low[x] = min(low[x], low[i]);
        }
        else if (instk[i])low[x] = min(low[x], index[i]);

    if (index[x] == low[x])
    {
        c.clear();
        while (!st.empty())
        {
            int a = st.top();
            st.pop();
            instk[a] = 0;
            c.push_back(a);
            if (index[a] == low[a])break;
        }
        cc.push_back(c);
    }

}