foo.cc: In function 'void dfs(int, int, int, int)':
foo.cc:28:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<g[x].size();i++)
              ~^~~~~~~~~~~~
foo.cc: In function 'void check(int, int)':
foo.cc:43:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<path[u][v].size();i++)
               ~^~~~~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:55:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d",&n,&s);
  ~~~~~^~~~~~~~~~~~~~
foo.cc:59:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d%d",&u,&v,&w);
   ~~~~~^~~~~~~~~~~~~~~~~~~

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