#include <iostream>
#include<fstream>
#include<vector>
#include<algorithm>
using namespace std;ifstream fin("ctc.in");ofstream fout("ctc.out");
int n,m,a,b,i,j,viz[100001],afis;vector<int>v[100001],topo,rsp[100001];
void dfs(int node){
    viz[node]=1;
    for(auto x:v[node]){
        if(!viz[x])dfs(x);
    }
    topo.push_back(node);
}
void ctc(int node){
    viz[node]=0;
    for(auto x:v[node]){
        if(viz[x])ctc(x);
    }
    rsp[afis].push_back(node);
}
int main()
{
    fin>>n>>m;
    for(i=1;i<=m;i++){
        fin>>a>>b;
        v[a].push_back(b);
    }
    for(i=1;i<=n;i++)if(!viz[i])dfs(i);
    topo.push_back(0);
    reverse(topo.begin(),topo.end());
    for(i=n;i>0;i--){
        if(!viz[topo[i]])continue;
        afis++;
        ctc(topo[i]);
    }
    fout<<afis<<'\n';
    for(i=1;i<=afis;i++){
        for(j=0;j<rsp[i].size();j++)fout<<rsp[i][j]<<' ';
        fout<<'\n';
    }
    return 0;
}