/in/foo.cc:2:16: warning: overflow in implicit constant conversion [-Woverflow]
 const int maxn=5000000000;
                ^~~~~~~~~~
/in/foo.cc: In function 'void build_max_heap(int*, int)':
/in/foo.cc:48:6: warning: unused variable 'heap_size' [-Wunused-variable]
  int heap_size=len;
      ^~~~~~~~~