#include <iostream>
#include <cstdio>
#include <vector>
#include <stack>
using namespace std;

vector<vector<int>> adjl;
vector<int> low;
stack<int> t;
vector<bool> popped;
vector<vector<int>> sccs;
int num = 0;

void dfs(int u)
{
	int numu = num++;
	low[u] = numu;
	t.push(u);
	for (auto v: adjl[u]) {
		if (popped[v]) continue;
		if (low[v] == -1) {
			dfs(v);
		}
		low[u] = min(low[u], low[v]);
	}
	if (low[u] == numu) {
		vector<int> scc;
		int top;
		do {
			top = t.top();
			t.pop();
			popped[top] = true;
			scc.push_back(top);
		} while (top != u);
		sccs.push_back(scc);
	}
}

int main()
{
	ios::sync_with_stdio(false);
	freopen("ctc.in", "r", stdin);
	freopen("ctc.out", "w", stdout);
	int n, m;
	cin >> n >> m;
	adjl.resize(n);
	for (int i = 0; i < m; i++) {
		int u, v;
		cin >> u >> v;
		u--, v--;
		adjl[u].push_back(v);
	}
	low.assign(n, -1);
	popped.resize(n);
	for (int i = 0; i < n; i++) {
		if (!popped[i]) {
			dfs(i);
		}
	}
	printf("%d\n", sccs.size());
	for (auto& scc: sccs) {
		for (auto u: scc) {
			printf("%d ", u+1);
		}
		printf("\n");
	}
	return 0;
}