#include <fstream>
#include <vector>
#include <queue>
//#include <priority_queue>

using namespace std;

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

const int N=1e5+1;
const int M=2e5+1;

int ctc[N],nc=1;
vector<int> a[N],a_t[N];
priority_queue<int> pq[N];
//queue<int> stiva;
int stiva[N],vf;
bool viz[N],viz_t[N];

void dfs(int x)
{
    viz[x]=1;
    for(auto y: a[x])
    {
        if(!viz[y]) dfs(y);
    }
    stiva[++vf]=x;
    //stiva.push(x);
}

void dfs_t(int x)
{
    viz_t[x]=1;
    pq[nc].push(-x);
    //ctc[x]=nc;
    for(auto y: a_t[x])
    {
        if(!viz_t[y]) dfs_t(y);
    }
}

int main()
{
    int n,m,x,y;
    in>>n>>m;
    for(int i=1; i<=m; i++)
    {
        in>>x>>y;
        a[x].push_back(y);
        a_t[y].push_back(x);
    }
    for(int i=1; i<=n; i++)
    {
        if(viz[i]==0) dfs(i);
    }
    while(vf>0)
    {
        if(viz_t[stiva[vf]]==0)
        {
            dfs_t(stiva[vf]);
            nc++;
        }
        vf--;
    }
    nc--;
    //out<<pq[1].top()<<" "<<pq[2].top()<<"\n\n";
    out<<nc<<"\n";
    for(int i=1; i<=nc; i++)
    {
        while(!pq[i].empty())
        {
            out<<-pq[i].top()<<" ";
            pq[i].pop();
        }
        out<<"\n";
    }
    return 0;
}