#include <fstream>
#include <vector>
#include <queue>
#define NMAX 100005

using namespace std;

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

vector <int> M[NMAX], T[NMAX], S, R[NMAX];
int n, m, result, visited[NMAX], mark[NMAX];

void DFS(int node)
{
    int i;
    visited[node] = 1;
    for(i = 0; i < M[node].size(); i++)
        if(visited[M[node][i]] == 0)
        DFS(M[node][i]);
    S.push_back(node);
}
void DFT(int node)
{
    int i;
    mark[node] = result;
    R[result].push_back(node);
    for(i = 0; i < T[node].size(); i++)
        if(mark[T[node][i]] == 0)
        {
            DFT(T[node][i]);
        }
}
int main()
{
    int i, j, x, y;
    fin >> n >> m;
    for(i = 1; i <= m; i++)
    {
        fin >> x >> y;
        M[x].push_back(y);
        T[y].push_back(x);
    }
    for(i = 1; i <= n; i++)
        if(visited[i] == 0)
        DFS(i);
    for(i = S.size() - 1; i >= 0; i--)
        if(mark[S[i]] == 0)
        {
            ++result;
            DFT(S[i]);
        }
    fout << result<< '\n';
    for(i = 1; i <= result; i++)
    {
        for(j = 0; j < R[i].size(); j++)
            fout << R[i][j] << ' ';
        fout << '\n';
    }
    return 0;
}