#include <fstream>
#include <bitset>
#include <vector>
#include <stack>
#define K 100002
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
int i,n,m,x,y,niv[K],low[K],f[K],nivel,ctc;
vector <int> v[K],sol[K];
stack <int> s;
void dfs(int nod){
    //low[nod]=cel mai mic nivel la care se poate ajunge din nod
    niv[nod]=low[nod]=++nivel;
    s.push(nod);
    f[nod]=1;
    for(auto vecin: v[nod])
        if(!niv[vecin]){ //nevizitat
            dfs(vecin);
            low[nod]=min(low[vecin],low[nod]);
        }else if(f[vecin]) //e in stiva deja
            low[nod]=min(low[vecin],low[nod]);

    if(niv[nod]==low[nod]){ //am gasit o ctc
        ctc++;
        int x=0;
        while(x!=nod){
            x=s.top();
            sol[ctc].push_back(x);
            f[x]=0;
            s.pop();
        }
    }
}
int main(){
    fin>>n>>m;
    for(i=1;i<=m;i++){
        fin>>x>>y;
        v[x].push_back(y);
    }
    for(i=1;i<=n;i++)
        if(!niv[i])
            dfs(i);
    fout<<ctc<<"\n";
    for(i=1;i<=ctc;i++){
        for(auto x :sol[i])
            fout<<x<<" ";
        fout<<"\n";
    }
    return 0;
}