#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#include <algorithm>

using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

const int NMAX = 100005;

int n, m;

int low_link[NMAX], ids[NMAX], onStack[NMAX];

stack<int>st;

vector<int>G[NMAX];
vector<vector<int>>sol;

void init(int n)
{
	for (int i = 1; i <= n; i++)
		ids[i] = -1;
	while (!st.empty()) st.pop();
}

void read()
{
	fin >> n >> m;
	while (m--)
	{
		int a, b;
		fin >> a >> b;
		G[a].push_back(b);
	}
	init(n);
}

void dfs(int u)
{
	static int value = 0;

	st.push(u);
	onStack[u] = true;
	ids[u] = low_link[u] = ++value;

	for (int v : G[u])
	{
		if (ids[v] == -1)
		{
			dfs(v);
			low_link[u] = min(low_link[u], low_link[v]);
		}
		else if (onStack[v])
			low_link[u] = min(low_link[u], low_link[v]);
	}

	if (ids[u] == low_link[u])
	{
		vector<int> v;
		while (!st.empty())
		{
			int nod = st.top();
			v.push_back(nod);
			onStack[nod] = false;
			low_link[nod] = ids[u];
			st.pop();

			if (nod == u) break;
		}
		sort(v.begin(), v.end());
		sol.push_back(v);
	}
}

void tarjan()
{
	for (int i = 1; i <= n; i++)
		if (ids[i] == -1)
			dfs(i);
}

void print(vector<int>& v)
{
	for (int e : v)
		fout << e << ' ';
	fout << '\n';
}

void solve()
{
	tarjan();
	fout << sol.size() << '\n';
	for (vector<int> v : sol)
		print(v);
}

int main()
{
	read();
	solve();
	return 0;
}