/in/foo.cc: In function 'int main()':
/in/foo.cc:20:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if (s.size()<=2) for (int i=0;i<s.size();i++) {
                                   ~^~~~~~~~~
/in/foo.cc:23:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if (s.size()>2) for (int i=s.size()-2;i<s.size();i++) {
                                        ~^~~~~~~~~