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

#define DIM 100010

using namespace std;

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

int n, m, level, ctcCount;

vector<int> L[DIM], ctcs[DIM];

bool vis[DIM];

int niv[DIM], low[DIM];

stack<int> st;

void CTC(int node) {

	niv[node] = low[node] = ++level;

	vis[node] = true;

	st.push(node);

	for (int i = 0; i < L[node].size(); i++) {

		int child = L[node][i];

		if (!vis[child])
			CTC(child);

		if (niv[child] > 0)
			low[node] = min(low[node], low[child]);

	}

	if (niv[node] <= low[node]) {

		ctcCount++;
		
		int x;

		do {

			x = st.top();
			niv[x] *= -1;
			
			ctcs[ctcCount].push_back(x);

			st.pop();


		} while (x != node);

	}

}

int main() {

	fin >> n >> m;

	for (int i = 1; i <= m; i++) {

		int x, y;

		fin >> x >> y;
		L[x].push_back(y);

	}

	for (int i = 1; i <= n; i++) {

		if (!vis[i])
			CTC(i);

	}

	fout << ctcCount << "\n";

	for (int i = 1; i <= ctcCount; i++) {

		for (int j = 0; j < ctcs[i].size(); j++)
			fout << ctcs[i][j] << " ";

		fout << "\n";

	}

	return 0;

}

//Miriam e tare!