/in/foo.cc: In function 'void solve()':
/in/foo.cc:16:40: warning: unused variable 'v' [-Wunused-variable]
 #define RED(i,u) for(int i = head[(u)],v; i != 0; i = ne[i])
                                        ^
/in/foo.cc:122:3: note: in expansion of macro 'RED'
   RED(j,i)
   ^~~