#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#include <algorithm>
#include <string>
using namespace std;

const int  NMAX = 100001;
int id=0, tot=0;
string resp="";
vector<int> graf[NMAX];
int ids[NMAX];
int low[NMAX];
bool onStack[NMAX];
stack<int> s[NMAX];

void DFS(int curr) {
	onStack[curr] = true;
	ids[curr] = ++id;
	low[curr] = id;
	s->push(curr);
	for (int i = 0; i < graf[curr].size(); i++) {
		if (ids[graf[curr][i]] == 0) {
			DFS(graf[curr][i]);
		}
		if (onStack[graf[curr][i]]) {
			low[curr] = min(low[curr], low[graf[curr][i]]);
		}
	}

	if (ids[curr] == low[curr]) {
		while (!s->empty()) {
			int node = s->top();
			resp += to_string(node);
			resp += " ";
			s->pop();
			onStack[node] = false;
			low[node] = ids[curr];
			if (node == curr) {
				break;
			}
		}
		tot++;
		resp += "\n";
	}
}

int main() {
	ifstream in("ctc.in");
	ofstream out("ctc.out");
	int n, m, x, y;
	in >> n >> m;

	for (int i = 0; i < m; i++) {
		in >> x >> y;
		graf[x].push_back(y);
	}

	/*for (int i = 1;i <= n; i++) {
		cout << i << ": ";
		for (int j = 0; j < graf[i].size(); j++) {
			cout << graf[i][j]<<" ";
		}
		cout << endl;
	}*/


	for (int i = 1; i <= n; i++) {
		if (ids[i] == 0) {
			DFS(i);
		}
	}
	
	out << tot << "\n" << resp;

	return 0;
	
}