/in/foo.cc: In function 'void Output(std::vector<Edge>&)':
/in/foo.cc:55:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<G.size();i++){
              ~^~~~~~~~~
/in/foo.cc: In function 'bool judge(std::vector<Edge>&, int)':
/in/foo.cc:62:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<G.size();i++){
              ~^~~~~~~~~