#include <cstdio>
#include <cstring>
#include <stack>
#include <vector>

using namespace std;

inline int next_int() {
	int d;
	scanf("%d", &d);
	return d;
}

const int V = 1 << 17;
const int E = 1 << 18;

int ec, eb[V], en[E], et[E];

int time, id[V], low[V], stacked[V];
stack<int> stk;
vector<vector<int> > scc;

void dfs(int u) {
	id[u] = low[u] = time++;
	stk.push(u);
	stacked[u] = true;
	for (int e = eb[u]; e != -1; e = en[e]) {
		int v = et[e];
		if (id[v] == -1) {
			dfs(v);
			low[u] = min(low[u], low[v]);
		} else if (stacked[u]) {
			low[u] = min(low[u], id[v]);
		}
	}
	if (id[u] == low[u]) {
		vector<int> c;
		do {
			c.push_back(stk.top());
			stacked[stk.top()] = false;
			stk.pop();
		} while (c.back() != u);
		scc.push_back(c);
	}
}

int main() {
	freopen("ctc.in", "r", stdin);
	freopen("ctc.out", "w", stdout);
	int n = next_int();
	int m = next_int();
	memset(eb, -1, sizeof eb);
	memset(id, -1, sizeof id);
	for (int i = 0; i < m; i++) {
		int u = next_int();
		int v = next_int();
		et[ec] = v;
		en[ec] = eb[u];
		eb[u] = ec++;
	}
	for (int i = 1; i <= n; i++) {
		if (id[i] == -1) {
			dfs(i);
		}
	}
	printf("%d\n", int(scc.size()));
	for (size_t i = 0; i < scc.size(); i++) {
		for (size_t j = 0; j < scc[i].size(); j++) {
			printf("%d ", scc[i][j]);
		}
		printf("\n");
	}
	return 0;
}