foo.cc: In function 'int dfs(int, int, int)':
foo.cc:32:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<a[now].size();i++){
              ~^~~~~~~~~~~~~~
foo.cc: In function 'void solve()':
foo.cc:57:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<a[root].size();i++){
               ~^~~~~~~~~~~~~~~

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