/in/foo.cc: In function 'bool OK()':
/in/foo.cc:17:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  return Next.x >= 0 && Next.x < str.size() && str[Next.x] != ' ';
                        ~~~~~~~^~~~~~~~~~~~
/in/foo.cc: In function 'int BFS(int)':
/in/foo.cc:31:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (now.x == str.size() - 1)
       ~~~~~~^~~~~~~~~~~~~~~~~
/in/foo.cc:36:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   else if (now.x > str.size() - 1)
            ~~~~~~^~~~~~~~~~~~~~~~