// 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> v;
vector<int> c[NMAX + 1];
int vis[NMAX + 1];
int visT[NMAX + 1];
int ctc;

void dfs(int node) {
    vis[node] = 1;
    for(auto it : G[node]) {
        if(!vis[it]) {
            dfs(it);
        }
    }
    v.push_back(node);
}

void dfsT(int node) {
    visT[node] = 1;
    c[ctc].push_back(node);
    for(auto it : GT[node]) {
        if(!visT[it]) {
            dfsT(it);
        }
    }
}

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(!vis[i]) {
            dfs(i);
        }
    }
    
    for(int i = n - 1; i >= 0; i--) {
        if(!visT[v[i]]) {
            ctc++;
            dfsT(v[i]);
        }
    }
    cout << ctc << '\n';
    for(int i = 1; i <= ctc; i++) {
        for(auto it : c[i]) {
            cout << it << ' ';
        }
        cout << '\n';
    }

}