#include <stdio.h>
#include <string.h>
using namespace std;
struct nod{
    int nr;
    nod* next;
}*First[2][100005],*TList[100005];
int N,M,TMax;
int TF[100005],Time;
bool Exist[2][100005],T[100005];
void Insert(int x,int y){
    if(First[0][x]==0){
        First[0][x]=new nod;
        First[0][x]->nr=y;
        First[0][x]->next=0;
    }
    else{
        nod *q=new nod;
        q->nr=y;
        q->next=First[0][x]->next;
        First[0][x]->next=q;
    }
    if(First[1][y]==0){
        First[1][y]=new nod;
        First[1][y]->nr=x;
        First[1][y]->next=0;
    }
    else{
        nod *q=new nod;
        q->nr=x;
        q->next=First[1][y]->next;
        First[1][y]->next=q;
    }
}

void InsertIntoT(int x,int y){
    if(TList[x]==0){
        TList[x]=new nod;
        TList[x]->nr=y;
        TList[x]->next=0;
    }
    else{
        nod *q=new nod;
        q->nr=y;
        q->next=TList[x]->next;
        TList[x]->next=q;
    }
}
void Read(){
    freopen("ctc.in","r",stdin);
    scanf("%d %d\n",&N,&M);
    int i,x,y;
    for(i=1;i<=M;i++){
        scanf("%d %d\n",&x,&y);
        Insert(x,y);
    }
    fclose(stdin);
}

void DF(int nr,int sw){
    int nra;
    Exist[sw][nr]=1;
    if(sw==1){
        if(Exist[0][nr]==1){
            InsertIntoT(TMax,nr);
            T[nr]=1;
        }

    }
    nod *q=First[sw][nr];
    while(q){
        nra=q->nr;
        if(T[nra]+Exist[sw][nra]==0)
            DF(nra,sw);
        q=q->next;
    }
}

void Solve(){
    int i,n=N;
    for(i=1;i<=n;i++){
        if(T[i]==0){
//            memset(Exist[0],0,sizeof(Exist[0]));
//            memset(Exist[1],0,sizeof(Exist[1]));
            TMax++;
            DF(i,0);
            DF(i,1);
        }
    }
}
void Write(nod *p){
    if(p){
        printf("%d ",p->nr);
        Write(p->next);
    }
    else
         printf("\n");
}
void write(int t[]){
    int i;
    for(i=1;i<=N;i++)
        printf("%d ",t[i]);
    printf("\n");
}
int main()
{
    Read();
    Solve();
    freopen("ctc.out","w",stdout);
    printf("%d\n",TMax);
    for(int i=1;i<=TMax;i++)
    Write(TList[i]);
    fclose(stdin);
    return 0;
}