/in/foo.cc: In function 'int main()':
/in/foo.cc:12:6: warning: unused variable 'in' [-Wunused-variable]
  int in = 0;
      ^~
/in/foo.cc: In function 'std::vector<int> X(int, std::vector<int>)':
/in/foo.cc:46:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < J.size(); i++)
                  ~~^~~~~~~~~~
/in/foo.cc:50:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < J.size(); i++)
                  ~~^~~~~~~~~~
/in/foo.cc:54:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if ((i + 1) < J.size())
        ~~~~~~~~^~~~~~~~~~