/in/foo.cc: In member function 'void FenwickTree::add(int, int)':
/in/foo.cc:16:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   16 |         while (idx < tree.size()) {
      |                ~~~~^~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:147:18: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17' [-Wc++17-extensions]
  147 |             auto [S, L] = seg_tree.query_range(1, X);
      |                  ^