#include <bits/stdc++.h>
#define oo 0x3f3f3f3f

using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
int n, m, number;
vector<int> graph[100001], transpose[100001];
vector<int> comps[100001];
vector<int> topologic;
bool visited[100001];

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

void dfs(int node)
{
  visited[node] = true;

  for(auto it : graph[node])
    if(!visited[it])
      dfs(it);

  topologic.push_back(node);
}

void dfst(int node, int number)
{
  visited[node] = false;
  comps[number].push_back(node);

  for(auto it : transpose[node])
    if(visited[it])
      dfst(it, number);
}

void solve()
{
  for(int i = 1;i <= n;++i)
    if(!visited[i])
      dfs(i);
  
  for(vector<int>::reverse_iterator it = topologic.rbegin();it != topologic.rend();++it)
    if(visited[(*it)])
      {
        ++number;
        dfst((*it), number);
      }
  g<<number<<'\n';
  for(int i = 1;i <= number;++i, g<<'\n')
    for(auto it : comps[i])
      g<<it<<" ";
}

int main()
{
  read();
  solve();
  return 0;
}