#include <iostream>
#include <fstream>
#include <queue>
#include <vector>
using namespace std;
ifstream in("cct.in");
ofstream out("cct.out");
vector <int> v[100005];
vector <int> v1[100005];
vector <int> sol1[100005];
queue <int> q;
int n,m,a1,b1,pl[100005],mins[100005],ind,ap[100005];
void sol(int t)
{
    int x;
    q.push(t);
    pl[t]=ind;
    ap[t]=1;
    while(!q.empty())
    {
        x=q.front();
        q.pop();
        for(auto i:v[x])
        {
            if(pl[i]!=pl[x])
            {
                pl[i]=ind;
                q.push(i);
            }
        }
    }
    q.push(t);
    mins[t]=ind;
    sol1[ind].push_back(t);
    while(!q.empty())
    {
        x=q.front();
        q.pop();
        for(auto i:v1[x])
        {
            if(mins[i]!=mins[x])
            {
                mins[i]=ind;
                if(pl[i]==ind)ap[i]=1,sol1[ind].push_back(i);
                q.push(i);
            }
        }
    }

}
int main()
{
    in>>n>>m;
    for(int i=1;i<=m;i++)
    {
        in>>a1>>b1;
        v[a1].push_back(b1);
        v1[b1].push_back(a1);
    }
    for(int i=1;i<=n;i++)
    {
        if(ap[i]==0)
        {
            ++ind;
            sol(i);
        }
    }
    out<<ind<<'\n';
    for(int i=1;i<=ind;i++)
    {
        for(auto j:sol1[i])out<<j<<' ';
        out<<'\n';
    }
    return 0;
}