#include <fstream>
#include <vector>
#include <stack>

using namespace std;

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

const int NMAX = 100001;

int n;
vector < int > V[NMAX]; // graph
vector < int > Vt[NMAX];
vector < int > A[NMAX]; // elements of strongly connected components
stack < int > S;
bool seen[NMAX];
bool seen_t[NMAX];
int idx; // the number of strongly connected components

void read()
{
    int m, x, y, i;
    fin >> n >> m;
    for (i = 1; i <= m; ++ i)
        {
         fin >> x >> y;
         V[x].push_back(y);
         Vt[y].push_back(x);
        }
}

void dfs(int node)
{
    vector < int > :: iterator it;
    seen[node] = true;
    for (it = V[node].begin(); it != V[node].end(); ++ it)
        if (!seen[*it])
            dfs(*it);
    S.push(node);
}

void end_time()
{
    int i;
    for (i = 1; i <= n; ++ i)
        if (!seen[i])
            dfs(i);
}

void dfs_t(int node)
{
    vector < int > :: iterator it;
    seen_t[node] = true;
    for (it = Vt[node].begin(); it != Vt[node].end(); ++ it)
        if (!seen_t[*it])
            dfs_t(*it);
    A[idx].push_back(node);
}

void tarjan()
{
    while (!S.empty())
        if (!seen_t[S.top()])
            {
             ++ idx;
             dfs_t(S.top());
            }
        else
            S.pop();
}

void print()
{
    int i;
    vector < int > :: iterator it;
    fout << idx << "\n";
    for (i = 1; i <= idx; ++ i)
        {
         for (it = A[i].begin(); it != A[i].end(); ++ it)
            fout << *it << " ";
         fout << "\n";
        }
}

int main()
{
    read();
    fin.close();
    end_time();
    tarjan();
    print();
    fout.close();
    return 0;
}