#include <bits/stdc++.h>
using namespace std;
const int MAXN = 500005;
vector<int> G[MAXN]; int dfn[MAXN], low[MAXN], col[MAXN], times;
bool instk[MAXN]; stack<int> stk; int btot;
vector<int> G2[MAXN], scc[MAXN]; int deg[MAXN];
void tarjan(int u) {
	dfn[u] = low[u] = ++times; instk[u] = 1; stk.push(u); for (int v : G[u]) {
		if (dfn[v] == 0) tarjan(v), low[u] = min(low[u], low[v]);
		else if (instk[v]) low[u] = min(low[u], dfn[v]);
	}
	if (low[u] == dfn[u]) {
		int y; btot++; do {
			y = stk.top(); stk.pop(); instk[y] = 0; scc[col[y] = btot].push_back(y);
		} while (y != u);
	}
}
int main() {
	int n, m; scanf("%d %d", &n, &m);
	for (int i = 1; i <= m; i++) {
		int u, v; scanf("%d %d", &u, &v); u++; v++;
		G[u].push_back(v);
	}
	for (int i = 0; i < n; i++) if (dfn[i] == 0) tarjan(i);
	for (int i = 0; i < n; i++) for (int v : G[i]) {
		if (col[i] != col[v]) G2[col[i]].push_back(col[v]), deg[col[v]]++;
	}
	queue<int> q; for (int i = 1; i <= btot; i++) if (deg[i] == 0) q.push(i);
	printf("%d\n", btot); while (q.empty() == 0) {
		int u = q.front(); q.pop();
		printf("%d", (int)scc[u].size()); for (int v : scc[u]) printf(" %d", v - 1); puts("");
		for (int v : G2[u]) if (--deg[v] == 0) q.push(v);
	}
}