#include <cstdio>
#include <vector>
#define nmax 100001
using namespace std;

typedef vector <int> A[nmax];
A a1,a2,v;
bool viz[nmax];

unsigned int n,m,x,y,i,j,nr,k,coada[nmax];

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);
        a1[x].push_back(y);
        a2[y].push_back(x);
    }
}

void dfs1(int i)
{
    viz[i]=1;
    for(unsigned int j=0;j<a1[i].size();j++)
        if(!viz[a1[i][j]])
            dfs1(a1[i][j]);
    coada[++k]=i;
}

void dfs2(int i)
{
    v[nr].push_back(i);
    viz[i]=0;
    for(unsigned int j=0;j<a2[i].size();j++)
        if(viz[a2[i][j]])
            dfs2(a2[i][j]);
}

int main()
{
    citire();
    for(i=1;i<=n;i++)
        if(!viz[i])
            dfs1(i);
    for(i=n;i;i--)
        if(viz[coada[i]])
            nr++,
            dfs2(coada[i]);
    printf("%d\n",nr);
    for(i=1;i<=nr;i++)
    {
        for(j=0;j<v[i].size();j++)
            printf("%d ",v[i][j]);
        printf("\n");
    }
    return 0;
}