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

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

vector<int> L[100001], LT[100001], ctc[100001];
int vis1[100001], vis2[100001];
vector<int> v;
int nr, n, m;

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

void dfs2(int nod) {
    ctc[nr].push_back(nod);
    vis2[nod] = 1;
    //cout << nod << ' ';
    for(auto vecin : LT[nod]) {
        if(!vis2[vecin]) {
            dfs2(vecin);
        }
    }
}

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