#include <iostream>
#include <fstream>
#include <vector>
#include <string.h>
#define N 100001
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
vector <int> v[N];
vector <int> ver[N];
vector <int> rez[N];
int viz[N],sir[N],k,l;
void dfs1(int x)
{
    viz[x]=1;
    for(int i=0;i<v[x].size();++i)
    if(!viz[v[x][i]])dfs1(v[x][i]);
    sir[++k]=x;
}
void dfs2(int x)
{
    viz[x]=1;
    for(int i=0;i<ver[x].size();++i)
    if(!viz[ver[x][i]])dfs2(ver[x][i]);
    rez[l].push_back(x);
}

int main()
{
    int n,m,i,x,y,j;
    f>>n>>m;
    for(i=1;i<=m;++i)
    {
        f>>x>>y;
        v[x].push_back(y);
        ver[y].push_back(x);

    }
    for(i=1;i<=n;++i)
        if(viz[i]==0) dfs1(i);
    memset(viz,0,sizeof(viz));
    for(i=k;i>=1;--i)
        if(viz[sir[i]]==0) {l++;dfs2(sir[i]);}
    g<<l<<'\n';
    for(i=1;i<=l;++i)
    {
        for(j=0;j<rez[i].size();++j)
        g<<rez[i][j]<<" ";
        g<<'\n';

    }
    return 0;
}