#include <bits/stdc++.h>

using namespace std;

const int NMAX = 100003;

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

void dfs(int node) {
	disc[node] = 1;
	for(int son : g[node]) {
		if(disc[son]) continue;
		dfs(son);
	}
	st.push(node);
}

void dfsr(int node) {
	disc[node] = 1;
	Q[SCC].push_back(node);
	for(int son : rg[node])
		if(!disc[son])
			dfsr(son);
}

// KOSARAJU
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);
		rg[y].push_back(x);
	}
	for(int i = 1; i <= n; i++)
		if(!disc[i])
			dfs(i);
			
	for(int i = 1; i <= n; i++) disc[i] = 0;

	while(!st.empty()) {
		int node = st.top();
		st.pop();
		if(!disc[node]) {
			SCC++;
			dfsr(node);-
		}
	}
	printf("%d\n", SCC);
	for(int i = 1; i <= SCC; i++) {
		for(int node : Q[i]) printf("%d ", node);
		puts("");
	}
	
}