/in/foo.cc: In function 'void dfs(std::vector<int>, int, int)':
/in/foo.cc:37:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<a.size();i++)
              ~^~~~~~~~~
/in/foo.cc:50:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if(cnt+son.size()-1>ans) return;
     ~~~~~~~~~~~~~~~~^~~~
/in/foo.cc:51:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<son.size();i++)
              ~^~~~~~~~~~~