/in/foo.cc: In function 'int main()':
/in/foo.cc:67:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(k>=0) lst=k<up[t].size()?up[t][k]:0;
                ~^~~~~~~~~~~~~
/in/foo.cc:68:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   else k=-k,lst=k<down[t].size()?down[t][k]:0;
                 ~^~~~~~~~~~~~~~~