/in/foo.cc: In function 'long long int dfs(int)':
/in/foo.cc:21:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if(pos==s.length())return 1;
     ~~~^~~~~~~~~~~~
/in/foo.cc:25:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<=dfss.length();i++){
              ~^~~~~~~~~~~~~~~