#include <fstream>
#include <vector>
using namespace std;
	
ifstream fin("ctc.in");
ofstream fout("ctc.out");

	
int n, m, q;	
int k, DUD[100006];
bool viz[100001];
	
vector <int> V1[100001];
vector <int> V2[100001];
vector <int> ctc[100001];


void DFS1(int nod){
	
    viz[nod] = 1;
	
    for(auto it : V1[nod])
        if(!viz[it])
            DFS1(it);
	
    DUD[++k] = nod;
}
	

void DFS2(int nod){
	
    viz[nod] = 0;
    ctc[q].push_back(nod);
	
    for(auto it : V2[nod])
        if(viz[it] == 1)
            DFS2(it);
}
	
	
int main(){
	
    fin >> n >> m;
	
    for(int i = 1; i <= m; i++) {

        int x, y;
        fin >> x >> y;
	
        V1[x].push_back(y);
        V2[y].push_back(x);
    }
	
	
    for(int i = 1; i <= n; i++)
        if(!viz[i])
            DFS1(i);
	
	
    for(int i = n; i >= 1; i--)
        if(viz[DUD[i]] == 1){
	
                q++;
                DFS2(DUD[i]);
            }
	
    fout << q << endl;
	
    for(int i = 1; i <= q; i++){
	
        for(auto it : ctc[i])
            fout << it << ' ';
	
        fout << endl;
    }
	
    return 0;
}