/in/foo.cc: In function 'std::__cxx11::string dfs(int)':
/in/foo.cc:17:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i=0;i<ss.size();i++)
                  ~^~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:54:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int i=1;i<it.second.size();i++)
                          ~^~~~~~~~~~~~~~~~~