foo.cc: In function 'int dfs(int, int, int)':
foo.cc:31:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int k=0;k<v[i].size();k++)
              ~^~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:39:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d",&n,&m);
  ~~~~~^~~~~~~~~~~~~~
foo.cc:40:27: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  for(int i=0;i<m;i++)scanf("%d%d%d",&a[i].u,&a[i].v,&a[i].l);
                      ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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