/in/foo.cc: In function 'void vdfs(long long int, long long int)':
/in/foo.cc:16:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<t[xb].l.size();i++)
              ~^~~~~~~~~~~~~~~
/in/foo.cc: In function 'long long int dfs(long long int, long long int, long long int)':
/in/foo.cc:23:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<t[xb].l.size();i++)
              ~^~~~~~~~~~~~~~~