// Source: https://usaco.guide/general/io

#include <bits/stdc++.h>
using namespace std;

const int NMAX = 1e5;
vector<int> G[NMAX + 1];
vector<int> GT[NMAX + 1];
vector<int> ctc[NMAX + 1];
int vis1[NMAX + 1], vis2[NMAX + 1], nr;
vector<int> v;

void dfs1(int node) {
    vis1[node] = 1;
    for(int vecin : G[node]) {
        if(!vis1[vecin]) {
            dfs1(vecin);
        }
    }
    v.push_back(node);
}

void dfs2(int node) {
    vis2[node] = 1;
    ctc[nr].push_back(node);
    for(int vecin : GT[node]) {
        if(!vis2[vecin]) {
            dfs2(vecin);
        }
    }
}

int main() {
    ifstream cin("ctc.in");
    ofstream cout("ctc.out");
	int n, m;
    cin >> n >> m;
    for(int i = 1; i <= m; i++) {
        int x, y;
        cin >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
    for(int i = 1; i <= n; i++) {
        if(!vis1[i]) {
            dfs1(i);
        }
    }
    for(int i = v.size() - 1; i >= 0; i--) {
        if(!vis2[v[i]]) {
            nr++;
            dfs2(v[i]);
        }
    }
    cout << nr << '\n';
    for(int i = 1; i <= nr; i++) {
        for(int x : ctc[i]) {
            cout << x << ' ';
        }
        cout << '\n';
    }
}