vector<vector<int> > g; // graph presented as adjacensy list
vector<bool> used; // we will mark visited vertexes
void dfs_visit(int v);

void dfs()
{
 for(int i=0; i<n; ++i)
  if (!used[i])
   dfs_visit(i);
}

void dfs_visit(int v)
{
 used[v] = true;
 for(int i=0; i<g[v].size(); ++i)
 {
  int to = g[v][i];
  if (!used[to])
   dfs_visit(to);
 }
}