#include <iostream>
#include <cstdio>
#include <deque>
#include <vector>

using namespace std;
FILE *fin, *fout;
vector <int>g[100000], gt[100000], gr[100000];
deque <int>s;
int n, ap[100000], nr=0;
void dfs(int a) {
    ap[a]=1;
    for (int i=0;i<g[a].size();i++) {
        int next=g[a][i];
        if (ap[next]==0) {
            dfs(next);
        }
    }
    s.push_back(a);
}
void dfss(int a) {
    ap[a]=2;
    gr[nr].push_back(a);
    for (int i=0;i<gt[a].size();i++) {
        int next=gt[a][i];
        if (ap[next]==1) {
            dfss(next);
        }
    }
}
int main()
{
    int m, a, b, i;
    fin=fopen("ctc.in" ,"r");
    fout=fopen("ctc.out" ,"w");
    fscanf(fin, "%d%d" ,&n ,&m);
    for (i=0;i<m;i++) {
        fscanf(fin, "%d%d" ,&a ,&b);
        g[a].push_back(b);
        gt[b].push_back(a);
    }
    for (i=1;i<=n;i++) {
        if (ap[i]==0) {
            dfs(i);
        }
    }
    while (!s.empty()) {
        if (ap[s.back()]==1) {
            //fprintf(fout, "%d   " ,s.front());
            nr++;
            dfss(s.back());
        }
        s.pop_back();
    }
    fprintf(fout, "%d\n" ,nr);
    for (i=1;i<=nr;i++) {
        for (int l=0;l<gr[i].size();l++) {
            fprintf(fout, "%d " ,gr[i][l]);
        }
        fprintf(fout, "\n");
    }
    cout << "Hello world!" << endl;
    return 0;
}