#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pr = pair <int, int>;
#define _1 first
#define _2 second
const int N = 1000010;
bool vis[N];
int deg[N], que[N];
int n, m, tot, top, cnt;
int col[N], dfn[N], low[N], stk[N];
vector <int> vec[N], scc[N], vec2[N];
void tarjan(int x) {
	dfn[x] = low[x] = ++tot;
	stk[++top] = x;
	vis[x] = 1;
	for (int y : vec[x])
		if (!dfn[y]) {
			tarjan(y);
			low[x] = min(low[x], low[y]);
		} else if (vis[y])
			low[x] = min(low[x], dfn[y]);
	if (dfn[x] == low[x]) {
		++cnt;
		for (; stk[top] ^ x; --top) {
			col[stk[top]] = cnt;
			vis[stk[top]] = 0;
			scc[cnt].emplace_back(stk[top]);
		}
		col[x] = cnt;
		vis[x] = 0;
		scc[cnt].emplace_back(x);
		--top;
	}
}
int main() {
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= m; ++i) {
		int u, v;
		scanf("%d%d", &u, &v);
		++u;
		++v;
		vec[u].emplace_back(v);
	}
	for (int i = 1; i <= n; ++i)
		if (!dfn[i])
			tarjan(i);
	printf("%d\n", cnt);
	for (int i = 1; i <= n; ++i)
		for (int j : vec[i])
			if (col[i] ^ col[j]) {
				vec2[col[i]].emplace_back(col[j]);
				++deg[col[j]];
			}
	tot = 0;
	for (int i = 1; i <= cnt; ++i)
		if (!deg[i])
			que[++tot] = i;
	for (int i = 1; i <= cnt; ++i) {
		int x = que[i];
		for (int y : vec2[x])
			if (!--deg[y])
				que[++tot] = y;
	}
	for (int i = 1; i <= cnt; ++i) {
		printf("%llu ", scc[que[i]].size());
		for (int j : scc[que[i]])
			printf("%d ", j - 1);
		puts("");
	}
	return 0;
}