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

using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
int n, m, number;
bool viz[100001];
vector<int> topo;
vector<int> result[100001];
vector<int> graf[100001], graft[100001];

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

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

  for(int vecin : graf[node])
    if(!viz[vecin])
      dfs(vecin);
  
  topo.push_back(node);
}

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

  for(int vecin : graft[node])
    if(viz[vecin])
      dfst(vecin); 
}

void solve()
{
  for(int i = 1;i <= n;++i)
    if(!viz[i])
      dfs(i);

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

  g<<number<<'\n';

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

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