#include <stdio.h>
#include <vector>
#include <queue>
using namespace std;
#define IN "ctc.in"
#define OUT "ctc.out"
#define NMAX 100005

FILE * fin=fopen(IN,"r");
FILE * fout=fopen(OUT,"w");

int n,m,componenta,k;
int viz[NMAX];
int postordine[NMAX];
vector<int> matrice[NMAX];
vector<int> graf[NMAX];
vector<int> transpus[NMAX];

void citire();
void dfs(int x);
void dfst(int x);
void afisare();

int main()
{
    int i;
    citire();
    for(i=1;i<=n;i++)
    {
        if(viz[i]==0)
            dfs(i);
    }
    for(i=n;i>=1;i--)
    {
        if(viz[postordine[i]]==1)
        {
            componenta++;
            dfst(postordine[i]);
        }
    }
    afisare();

    fclose(fin);
    fclose(fout);
    return 0;
}

void citire()
{
    int i,x,y;
    fscanf(fin,"%d%d",&n,&m);
    for(i=1;i<=m;i++)
    {
        fscanf(fin,"%d%d",&x,&y);
        graf[x].push_back(y);
        transpus[y].push_back(x);
    }
}

void dfs(int x)
{
    int i,nod;
    viz[x]++;
    for(i=0;i<graf[x].size();i++)
    {
        nod=graf[x][i];
        if(viz[nod]==0)
            dfs(nod);
    }
    postordine[++k]=x;
}

void dfst(int x)
{
    int i,nod;
    viz[x]++;
    for(i=0;i<transpus[x].size();i++)
    {
        nod=transpus[x][i];
        if(viz[nod]==1)
            dfst(nod);
    }
    matrice[componenta].push_back(x);
}

void afisare()
{
    int i,j;
    fprintf(fout,"%d\n",componenta);
    for(i=1;i<=componenta;i++)
    {
        fprintf(fout,"%d",matrice[i][0]);
        for(j=1;j<matrice[i].size();j++)
            fprintf(fout," %d",matrice[i][j]);
        fprintf(fout,"\n");
    }
}