#include <bits/stdc++.h>
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
int drum[100001],n,nrcomponente,nr,m; bool viz[100001]; vector <int> adia[100001],adia2[100001],componenta[100001];

void dfs(int varf){
 if(!viz[varf]){ viz[varf]=1;
 for(int it : adia[varf]) dfs(it);
 drum[++nr]=varf;
 }
}

void dfs2(int varf){
 if(viz[varf]){ viz[varf]=0;
 for(int it : adia2[varf])dfs2(it);
 componenta[nrcomponente].push_back(varf);
 }
}
int main()
{
    fin>>n>>m; int x,y,i; while(fin>>x>>y)adia[x].push_back(y),adia2[y].push_back(x);

    for(i=1;i<=n;i++)dfs(i);
    for(i=n;i>=1;i--)if(viz[drum[i]]){nrcomponente++; dfs2(drum[i]);}

    fout<<nrcomponente<<'\n';
    for(i=1;i<=nrcomponente;i++){for(int it : componenta[i])fout<<it<<" "; fout<<'\n';}
    return 0;
}