#include <iostream>
#include <fstream> 
#include <vector>
#include <algorithm>
using namespace std;

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

const int maxN = 1e5 + 5;

vector <int> g[maxN];
vector <int> gt[maxN];

vector <int> top;
int componenta[maxN], aparitii[maxN];
int check[maxN];

void sortTop (int node) {
    check[node] = -1;
    for(int next : g[node])
        if(check[next] == 0)
            sortTop(next);
    
    top.push_back(node);
}

void dfsG(int node, int cnt) {
    check[node] = -cnt;
    aparitii[node] = 1;
    for(int next : g[node])
        if(check[next] != -cnt)
            dfsG(next, cnt);
}

void dfsGT (int node, int cnt) {
    check[node] = cnt;
    aparitii[node] += 1;
    for(int next : gt[node])
        if(check[next] != cnt)
            dfsGT(next, cnt);
    if(aparitii[node] == 2) {
        componenta[node] = cnt;
    }
}

int main()
{
    int n, m; fin >> n >> m;
    for(int i = 1; i <= m; ++i) {
        int u, v; fin >> u >> v;
        g[u].push_back(v);
        gt[v].push_back(u);
    }
       
    for(int i = 1; i <= n; ++i) {
        if(check[i] == false)
        sortTop(i);
    }
    
    reverse(top.begin(), top.end());
   
    for(int i = 1; i <= n; ++i)
        check[i] = 0;
    
    int cnt = 0;
    for(int i = 0; i < top.size(); ++i) {
        if(componenta[top[i]] == 0) {
            cnt += 1;
            dfsG(top[i], cnt);
            dfsGT(top[i], cnt);
        }
        
    }
    
    fout << cnt << "\n";
    for(int k = 1; k <= cnt; ++k, fout << "\n")
        for(int i = 1; i <= n; ++i)
            if(componenta[i] == k)
                fout << i << " ";
                
    return 0;
}