/in/foo.cc: In function 'int main(int, char**)':
/in/foo.cc:21:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<L.size(); i++){
               ~^~~~~~~~~
/in/foo.cc:39:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0; i<L.size(); i++){
                ~^~~~~~~~~