/in/foo.cc: In function 'void addedge(int, int)':
/in/foo.cc:28:2: error: reference to 'next' is ambiguous
  next[++t]=first[s];
  ^~~~
/in/foo.cc:21:14: note: candidates are: int next [40005]
 int first[N],next[M],to[M],from[M],t;
              ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/algorithm:61,
                 from /in/foo.cc:3:
/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:45:33: error: reference to 'next' is ambiguous
  for(int i=first[x],v=to[i];i;i=next[i],v=to[i])
                                 ^~~~
/in/foo.cc:21:14: note: candidates are: int next [40005]
 int first[N],next[M],to[M],from[M],t;
              ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/algorithm:61,
                 from /in/foo.cc:3:
/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
     ^~~~