#include <iostream>
#include <fstream>
#include <stack>
#include <vector>
#include <bitset>
#define NMAX 100005
using namespace std;

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

int n, m, indecs, ind[NMAX], lowlink[NMAX], comps;
vector <int> g[NMAX], ctc[NMAX];
stack <int> steve;
bitset <NMAX> inst;

void tarjan (int node) {
	++indecs;
	ind[node] = indecs;
	lowlink[node] = indecs;
	//cout << node << " ";
	inst[node] = 1;
	steve.push(node);
	for (int i = 0; i < g[node].size(); ++i) {
		if (!ind[g[node][i]]) {
			tarjan(g[node][i]);
			lowlink[node] = min(lowlink[node], lowlink[g[node][i]]);
		}
		else
		if (inst[g[node][i]]) {
			lowlink[node] = min(lowlink[node], lowlink[g[node][i]]);
		}
	}
	if (ind[node] == lowlink[node]) {
		int x;
		++comps;
		do {
			x = steve.top();
			steve.pop();
			inst[x] = 0;
			ctc[comps].push_back(x);
		}while (x != node);
	}
}

int main ()
{
	fin >> n >> m;
	int x, y;
	for (int i = 1; i <= m; ++i) {
		fin >> x >> y;
		g[x].push_back(y);
	}
	for (int i = 1; i <= n; ++i) {
		if (!ind[i]) {
			tarjan(i);
		}
	}
	fout << comps << '\n';
	for (int i = comps; i >= 1; --i) {
		for (int j = ctc[i].size() - 1; j >= 0 ; --j) {
			fout << ctc[i][j] << " ";
		}
		fout << '\n';
	}
	/*while (steve.size()) {
		cout << steve.top() << " ";
		steve.pop();
	}*/
	
	fin.close();
	fout.close();
	return 0;
}