#include <iostream>
#include <fstream>
#include <stack>
#include <vector>
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
vector <int > nodes[100005];
vector <int > nodes2[100005];
vector <int > ctc[100005];
stack < int > st;
int viz[100005], n, m;
void dfs(int node){
    viz[node]++;
    for (auto &it : nodes[node]) {
        if(!viz[it]){
            dfs(it);
        }
    }
    st.push(node);
}
void dfst(int node,int nr){
    viz[node]++;
    for (auto &it : nodes2[node]) {
        if(viz[it]== 1){
            dfst(it,nr);
        }
    }
    ctc[nr].push_back(node);
}
int main()
{
     fin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int x, y;
        fin >> x >> y;
        nodes[x].push_back(y);
        nodes2[y].push_back(x);
    }
    for (int i = 1; i <= n; ++i) {
        if(!viz[i]){
            dfs(i);
        }
    }
    int nr = 0;
    while(!st.empty())
    {
        int top = st.top();
        st.pop();
        if(viz[top] == 1)
        {
            nr++;
            dfst(top,nr);
        }
    }
    fout << nr << "\n";
    for(int i = 1; i <= nr; i++)
    {
         for(auto &v : ctc[i])
        fout << v << " ";
        fout << endl;
    }



    return 0;
}