#include <bits/stdc++.h>

using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
int n, m, x, y, number;
vector<int> graf[100001], transpus[100001];
vector<int> topologic;
vector<int> comp[100001];
bool viz[100001];


void read()
{
  f>>n>>m;
  for(int i = 0;i < m;++i)
    f>>x>>y, graf[x].push_back(y), transpus[y].push_back(x);
}

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

  for(auto it : graf[node])
    if(!viz[it])
      dfs(it);

  topologic.push_back(node);
}

void dfst(int node)
{
  viz[node] = false;
  comp[number].push_back(node);

  for(auto it : transpus[node])
    if(viz[it])
      dfst(it);
}

void solve()
{
  memset(viz, false, sizeof(viz));

  for(int i = 1;i <= n;++i)
    if(!viz[i])
      dfs(i);
  for(vector<int>::reverse_iterator it = topologic.rbegin();it != topologic.rend();++it)
    if(viz[*it])
      ++number, dfst(*it);

  g<<number<<'\n';
  for(int i = 1;i <= number;++i, g<<'\n')
    for(auto it : comp[i])
      g<<it<<" ";
}

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