#include <stdio.h>
#include <vector>
#include <stack>

#define maxdim 100005

using namespace std;

int n, m, p;
int lowest[maxdim], ind[maxdim], inSt[maxdim];
vector<int> G[maxdim];
vector<vector<int>> sol;
stack<int> st;

void dfs(int nod) {
	lowest[nod] = ind[nod] = ++p;
	st.push(nod); inSt[nod] = 1;
	
	for (int son : G[nod]) {
		
		if (!lowest[son]) {
			dfs(son);
			lowest[nod] = min(lowest[nod], lowest[son]);
		} else {
			if (inSt[son]) {
				lowest[nod] = min(lowest[nod], ind[son]);
			}
		}
	}
	
	if (lowest[nod] == ind[nod]) {
		vector<int> crt; int x;
		do {
			x = st.top(); st.pop(); inSt[x] = 0;
			crt.push_back(x);
		} while (nod != x);
		sol.push_back(crt);
	}
}

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 (!lowest[i]) {
			dfs(i);
		}
	}
	
	printf("%d\n", (int) sol.size());
	for (vector<int> &crt : sol) {
		for (int nod : crt) {
			printf("%d ", nod);
		}
		printf("\n");
	}

	return 0;
}