#include <queue>
#include <iostream>
#include <fstream>
#include <stack>

using namespace std;

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

#define NMax 100005
vector <int> G[NMax];
vector <int> GT[NMax];
vector <int> result[NMax];
int n,m,counter;
stack<int> S;
int *visited;
void read()
{
    counter = 0;
    f>>n>>m;
    visited = new int[NMax];
    for(int i = 0; i<=n+1;i++)
        visited[i] = 0;
    for(int i=1;i<=m;i++)
    {

        int x,y;
        f>>x>>y;
        G[x].push_back(y);
        GT[y].push_back(x);
    }
}
void showList()
{
    cout<<"n: "<<n<<endl;
    for(int i=1;i<=n;i++)
    {
        cout<<i<<": ";
        for(int j=0;j<GT[i].size();j++)
            cout<<GT[i][j]<<" ";
        cout<<endl;
    }
}
void DFS(int node)
{

    visited[node] = 1;
    //zone 1
    for(int i=0;i<G[node].size();i++)
    {
        //zone 2
        int neighbour = G[node][i];
        if(!visited[neighbour])
          DFS(neighbour);

        //zone 3
    }

    S.push(node);
    //zone 4
}
void DFS_T(int node)
{
    visited[node] = 2;
    result[counter].push_back(node);
    cout<<counter<<": "<<node<<"\n";
    for(int i=0;i<GT[node].size();i++)
    {
        int neighbour = GT[node][i];
        if(visited[neighbour] == 1)
            DFS_T(neighbour);
    }
}
void Solution()
{
    for(int i=1;i<=n;i++)
    {
        if(!visited[i])
            DFS(i);
    }
    while(!S.empty())
    {
        int node  = S.top();
        //cout<<node<<" ";
        if(visited[node] == 1)
        {
            counter++;
            DFS_T(node);
        }
        S.pop();
    }
}
void printResult()
{
    g<<counter<<"\n";
    for(int i=1;i<=counter;i++)
        {
            for(int j=0;j<result[i].size();j++)
                g<<result[i][j]<<" ";
            g<<endl;
        }
}
int main()
{
    read();
    //showList();
    Solution();
    printResult();
    return 0;
}