/in/foo.cc: In function 'long long int Sum(std::vector<Node>&)':
/in/foo.cc:22:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<a.size(); i++)
               ~^~~~~~~~~
/in/foo.cc: In function 'int Solve(std::vector<Node>&, int, int)':
/in/foo.cc:33:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<a.size(); i++)
               ~^~~~~~~~~
/in/foo.cc:39:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^