/in/foo.cc: In function 'void addedge(int, int)':
/in/foo.cc:36:2: error: reference to 'next' is ambiguous
  next[cc]=first[u];
  ^~~~
/in/foo.cc:33:20: note: candidates are: int next [600005]
 int cc,first[MAXN],next[MAXM],to[MAXM],from[MAXM];
                    ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:16:
/usr/include/c++/6/bits/stl_iterator_base_funcs.h:205:5: note:                 template<class _ForwardIterator> _ForwardIterator std::next(_ForwardIterator, typename std::iterator_traits<_Iter>::difference_type)
     next(_ForwardIterator __x, typename
     ^~~~
/in/foo.cc: In function 'void tarjan(int)':
/in/foo.cc:68:25: error: reference to 'next' is ambiguous
  for(int i=first[x];i;i=next[i])
                         ^~~~
/in/foo.cc:33:20: note: candidates are: int next [600005]
 int cc,first[MAXN],next[MAXM],to[MAXM],from[MAXM];
                    ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:16:
/usr/include/c++/6/bits/stl_iterator_base_funcs.h:205:5: note:                 template<class _ForwardIterator> _ForwardIterator std::next(_ForwardIterator, typename std::iterator_traits<_Iter>::difference_type)
     next(_ForwardIterator __x, typename
     ^~~~
/in/foo.cc: In function 'void dfs1(int)':
/in/foo.cc:92:27: error: reference to 'next' is ambiguous
  for(int i=first[now];i;i=next[i])
                           ^~~~
/in/foo.cc:33:20: note: candidates are: int next [600005]
 int cc,first[MAXN],next[MAXM],to[MAXM],from[MAXM];
                    ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:16:
/usr/include/c++/6/bits/stl_iterator_base_funcs.h:205:5: note:                 template<class _ForwardIterator> _ForwardIterator std::next(_ForwardIterator, typename std::iterator_traits<_Iter>::difference_type)
     next(_ForwardIterator __x, typename
     ^~~~
/in/foo.cc: In function 'void dfs2(int)':
/in/foo.cc:110:27: error: reference to 'next' is ambiguous
  for(int i=first[now];i;i=next[i])
                           ^~~~
/in/foo.cc:33:20: note: candidates are: int next [600005]
 int cc,first[MAXN],next[MAXM],to[MAXM],from[MAXM];
                    ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:16:
/usr/include/c++/6/bits/stl_iterator_base_funcs.h:205:5: note:                 template<class _ForwardIterator> _ForwardIterator std::next(_ForwardIterator, typename std::iterator_traits<_Iter>::difference_type)
     next(_ForwardIterator __x, typename
     ^~~~