#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int n, m, dfx = 0, tp = 0, sct = 0, hd[500010], e[500010][2], dfn[500010], low[500010], scc[500010], st[500010];
bool bk[500010];
vector<int> ans[500010];
void dfs(int u){
	int i, v, tmp = tp;
	dfn[u] = ++dfx; low[u] = dfn[u]; st[++tp] = u; bk[u] = true;
	for(i = hd[u]; i > 0; i = e[i][0]){
		v = e[i][1];
		if(dfn[v] == 0){
			dfs(v);
			low[u] = min(low[u], low[v]);
		}else if(bk[v]) low[u] = min(low[u], dfn[v]);
	}
	bk[u] = false;
	if(low[u] >= dfn[u]){
		sct++;
		while(tp > tmp){
			v = st[tp--];
			scc[v] = sct; ans[sct].push_back(v);
		}
	}
}
int main()
{
	int i, j, u, v;
	scanf("%d%d", &n, &m);
	for(i = 1; i <= n; i++) hd[i] = 0, dfn[i] = 0, bk[i] = false;
	for(i = 1; i <= m; i++){
		scanf("%d%d", &u, &v); u++; v++;
		e[i][0] = hd[u]; e[i][1] = v; hd[u] = i;
	}
	for(i = 1; i <= n; i++){
		if(dfn[i] == 0) dfs(i);
	}
	printf("%d\n", sct);
	for(i = sct; i > 0; i--){
		printf("%d ", ans[i].size());
		for(j = 0; j < ans[i].size(); j++) printf("%d ", ans[i][j] - 1);
		printf("\n");
	}
	return 0;
}