#include<fstream>
#include<vector>
#include<deque>
#define nx 100007
using namespace std;
int viz[nx],ord[nx],n,m,i,k,x,y;
vector<int>v[nx],t[nx],sol[nx];
deque<int>d;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

void citire()
{
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        v[x].push_back(y);
        t[y].push_back(x);
    }
}

void df1(int x)
{
    viz[x]=1;
    for(int j=0;j<v[x].size();j++)if(!viz[v[x][j]])df1(v[x][j]);
    d.push_back(x);
}

void df2(int x)
{
    viz[x]=1;
    sol[k].push_back(x);
    for(int j=0;j<t[x].size();j++)if(!viz[t[x][j]])df2(t[x][j]);
}

void afisare()
{
    fout<<k<<'\n';
    for(i=1;i<=k;i++)
    {
        for(int j=0;j<sol[i].size();j++)fout<<sol[i][j]<<' ';
        fout<<'\n';
    }
}

int main()
{
    citire();

    for(i=1;i<=n;i++)if(!viz[i])df1(i);
    for(i=1;i<=n;i++)viz[i]=0;
    while(!d.empty())
    {
        x=d.back(),d.pop_back();
        if(!viz[x])
        {
            k++;
            df2(x);
        }
    }

    afisare();
    return 0;
}