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

ifstream fin("ctc.in");
ofstream fout("ctc.out");

#define NMAX 500005

int n, m, viz[NMAX];
vector<int> s;
vector<int> v[NMAX], vp[NMAX];
vector<vector<int>> ans;

void dfs(int nod) {
    viz[nod] = 1;

    for (auto it: v[nod]) {
        if (viz[it]) continue;
        dfs(it);
    }
    s.push_back(nod);
}

void dfs2(int nod, vector<int> &c) {
    viz[nod] = 1;
    c.push_back(nod);
    for (auto it: vp[nod]) {
        if (viz[it]) continue;
        
        dfs2(it, c);
    }
}

int main() {
    
    fin >> n >> m;
    
    for (int i = 1; i<=m; i++) {
        int x, y;
        fin >> x >> y;
        v[x].push_back(y);
        vp[y].push_back(x);
    }
    
    for (int i = 1; i<=n; i++) {
        if (viz[i]) continue;
        dfs(i);
    }
    
    memset(viz, 0, sizeof(viz));
    
    while (!s.empty()) {
        if (viz[s.back()]) {
            s.pop_back();
            continue;
        }
        
        vector<int> c;
        dfs2(s.back(), c);
        ans.push_back(c);
    }
    
    fout << ans.size() << "\n";
    for (auto comp: ans) {
        for (auto nod: comp) {
            fout << nod << " ";
        }
        fout << '\n';
    }
    
    return 0;
}