#include<cstdio>
#include<vector>
#include<deque>
using namespace std;
int n,m,i,j,k,l,x,y,viz[100001],p1[100001],p2[100001];
vector<int>v[100001],t[100001],sol[100001];
deque<int>d;

void comp_tare_conex()
{
    k++;
    for(l=1;l<=n;l++)if(p1[l]+p2[l]==4*i-1)sol[k].push_back(l),viz[l]=1;
}

void bf1()
{
    d.push_back(i);
    p1[i]=2*i-1;
    while(!d.empty()){
        x=d.front();
        d.pop_front();
        for(j=0;j<v[x].size();j++)
        if(p1[v[x][j]]!=2*i-1 && viz[v[x][j]]==0)p1[v[x][j]]=2*i-1,d.push_back(v[x][j]);
    }
}

void bf2()
{
    d.push_back(i);
    p2[i]=2*i;
    while(!d.empty()){
        x=d.front();
        d.pop_front();
        for(j=0;j<t[x].size();j++)
        if(p2[t[x][j]]!=2*i && viz[t[x][j]]==0)p2[t[x][j]]=2*i,d.push_back(t[x][j]);
    }
}

void ver()
{
    bf1();
    bf2();
    for(j=1;j<=n;j++)if(p1[j]+p2[j]==4*j-1){comp_tare_conex();break;}
}

void citire()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
    scanf("%d %d",&n,&m);
    for(i=1;i<=m;i++)scanf("%d %d",&x,&y),v[x].push_back(y),t[y].push_back(x);
}

void afisare()
{
    printf("%d\n",k);
    for(i=1;i<=k;i++){
      for(j=0;j<sol[i].size();j++)printf("%d ",sol[i][j]);
        printf("\n");
          }
}

int main()
{
    citire();
    for(i=1;i<=n;i++)if(viz[i]==0)ver();
    afisare();
    return 0;
}