#define DM 100001
#include <fstream>
#include <stack>
#include <vector>
using namespace std;
 
ifstream fi ("ctc.in");
ofstream fo ("ctc.out");
int n, m, a, b, idx, cnt;
stack <int> s;
vector <int> ctc[DM];
class Node {
	public:
		bool stack = false;
		int idx = -1, low;
		vector <int> edges;
 
		void addNode(int x) {
			edges.push_back(x);
		}
} v[DM];
 
void connect_component(int x) {
	v[x].idx = v[x].low = ++idx;
	v[x].stack = true;
	s.push(x);
	for (auto i:v[x].edges) {
		if (v[i].idx == -1) {
			connect_component(i);
			v[x].low = min(v[x].low, v[i].low);
		} else if (v[i].stack && v[i].idx < v[x].idx) {
			v[x].low = min(v[x].low, v[i].idx);
		}
	}
	if (v[x].idx == v[x].low) {
		while (1) {
			a = s.top();
			s.pop();
			ctc[cnt].push_back(a);
			v[a].stack = false;
			if (a == x)
				break;
		}
		++cnt;
	}
}
 
int main() {
	fi >> n >> m;
	for (int i = 1; i <= m; ++i) {
		fi >> a >> b;
		v[a].addNode(b);
	}
	for (int i = 1; i <= n; ++i)
		if (v[i].idx == -1)
			connect_component(i);
	fo << cnt << '\n';
	for (int i = 0; i < cnt; ++i)
		for (auto j:ctc[i])
			fo << j << " \n"[j==ctc[i].back()];
	return 0;
}