#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

const int N = 5e5 + 5;

struct edge {
	int to, Next;

	edge() {}
	edge(int to, int Next): to(to), Next(Next) {}
} G[N << 1];

int n, m, head[N], cnt;

inline void add_edge(int u, int v) {
	G[++cnt] = edge(v, head[u]);
	head[u] = cnt;
}

stack <int> st;

int dfn[N], low[N], tot;

bitset <N> vis;
vector <vector <int> > ans;

inline void Tarjan(int u) {
	st.push(u);
	vis[u] = true;
	dfn[u] = low[u] = ++tot;
	for (int i = head[u]; i; i = G[i].Next) {
		int v = G[i].to;
		if (!dfn[v]) {
			Tarjan(v);
			low[u] = min(low[u], low[v]);
		} else if (vis[v]) {
			low[u] = min(low[u], dfn[v]);
		}
	}
	if (dfn[u] == low[u]) {
		vector <int> vec;
		while (!st.empty()) {
			int v = st.top();
			st.pop();
			vis[v] = false;
			vec.emplace_back(v);
			if (u == v) {
				break;
			}
		}
		ans.emplace_back(vec);
	}
}

int main() {
	#ifdef LOCAL
		assert(freopen("test.in", "r", stdin));
		assert(freopen("test.out", "w", stdout));
	#endif
	ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
	cin >> n >> m;
	while (m--) {
		int u, v;
		cin >> u >> v;
		add_edge(u, v);
	}
	for (int i = 0; i < n; ++i) {
		if (!dfn[i]) {
			Tarjan(i);
		}
	}
	cout << ans.size() << "\n";
	for (auto vec: ans) {
		cout << vec.size() << " ";
		for (auto u: vec) {
			cout << u << " ";
		}
		cout << "\n";
	}
	return 0;
}