#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define ar array
#define vt vector
#define pq priority_queue
#define pu push
#define pub push_back
#define em emplace
#define emb emplace_back

#define all(x) x.begin(), x.end()
#define allr(x) x.rbegin(), x.rend()
#define allp(x, l, r) x.begin() + l, x.begin() + r
#define len(x) (int)x.size()

using namespace std;
using namespace __gnu_pbds;

using ll = long long;
using ld = long double;
using ull = unsigned long long;

template <class T, size_t N>
void re(array <T, N>& x);
template <class T> 
void re(vt <T>& x);

template <class T> 
void re(T& x) {
    cin >> x;
}

template <class T, class... M> 
void re(T& x, M&... args) {
    re(x); re(args...);
}

template <class T> 
void re(vt <T>& x) {
    for(auto& it : x)
        re(it);
}

template <class T, size_t N>
void re(array <T, N>& x) {
    for(auto& it : x)
        re(it);
}

template <class T, size_t N>
void wr(array <T, N> x);
template <class T> 
void wr(vt <T> x);

template <class T> 
void wr(T x) {
    cout << x;
}

template <class T, class ...M>  void wr(T x, M... args) {
    wr(x), wr(args...);
}

template <class T> 
void wr(vt <T> x) {
    for(auto it : x)
        wr(it, ' ');
}

template <class T, size_t N>
void wr(array <T, N> x) {
    for(auto it : x)
        wr(it, ' ');
}


inline void Open(const string Name) {
    #ifndef ONLINE_JUDGE
        (void)!freopen((Name + ".in").c_str(), "r", stdin);
        (void)!freopen((Name + ".out").c_str(), "w", stdout);
    #endif
}

void solve() {
    /* Tarjan's algorithm */
    function <void(int)> dfs;
    int n, m; re(n, m);
    vt <vt <int>> adj(n), res;
    vt <int> low_link(n), index(n);
    vt <bool> on_stack(n);
    stack <int> st;
    for (int i = 0; i < m; ++i) {
        int u, v; re(u, v);
        --u, --v;
        adj[u].emb(v);
    }

    /* Low-Link Value
       The low-link value of a node is the smallest [lowest] node
       id reachable from that node when doing a DFS (including itself)

       All Strongly Connected Components have their low-link value the same.
    */

    int idx = 0;
    dfs = [&](int u) {
        index[u] = ++idx;
        low_link[u] = index[u];
        st.push(u);
        on_stack[u] = true;

        for (int v : adj[u]) {
            if (index[v] == 0) {
                // update the low-link value
                dfs(v);
                low_link[u] = min(low_link[u], low_link[v]);
            } else if (on_stack[v]) {
                //update the low-link value
                low_link[u] = min(low_link[u], low_link[v]);
            }
        }

        /* when we have the same low-link value as the index 
           we know that here lies the start of a Strongly Connected Component
           and we empty the stack.
        */
        if (low_link[u] == index[u]) {
            vt <int> tmp;
            int top;
            do {
                top = st.top();
                tmp.emb(top + 1);
                on_stack[top] = false;
                st.pop();
            } while(top != u);
            res.emb(tmp);
        }
    };

    for (int u = 0; u < n; ++u)
        if (index[u] == 0) {
            dfs(u);
        }

    wr(len(res), '\n');
    for (int i = 0; i < len(res); ++i)
        wr(res[i], '\n');
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    Open("ctc");

    int t = 1;
    for(;t;t--) {
        solve();
    }
    
    return 0;
}