#include <bits/stdc++.h>

using namespace std;

const int NMAX = 100003;

int n, m, timer,SCC;
int disc[NMAX], low[NMAX];
bool InStack[NMAX];
vector<int> g[NMAX], Q[NMAX];
stack<int> st;

void dfs(int node, int parent) {
	disc[node] = low[node] = ++timer;
	InStack[node] = 1;
	st.push(node);
	for(int son : g[node]) {
		if(!disc[son]) {
			dfs(son, node);
			low[node] = min(low[node], low[son]);
		} else if(InStack[son]) {
			low[node] = min(low[node], disc[son]);
		}
	}

	if(low[node] == disc[node]) {
		SCC++;
		while(st.top() != node) {
			int w = st.top();
			Q[SCC].push_back(w);
			InStack[w] = 0;
			st.pop();
		}
		Q[SCC].push_back(st.top());
		InStack[st.top()] = 0;
		st.pop();
	}
}

int main() {
	freopen("ctc.in", "r", stdin);
	freopen("ctc.out", "w", stdout);
	scanf("%d %d", &n, &m);
	for(int i = 1; i <= m; i++) {
		int x, y;
		scanf("%d %d", &x, &y);
		g[x].push_back(y);
	}
	
	for(int i = 1; i <= n; i++)
		if(!disc[i])
			dfs(i, -1);
	printf("%d\n", SCC);
	for(int i = 1; i <= SCC; i++) {
		for(int node : Q[i]) printf("%d ", node);
		puts("");
	}
	return 0;
}