foo.cc: In function 'int main()':
foo.cc:31:6: warning: unused variable 'tang' [-Wunused-variable]
   31 |  int tang=1;
      |      ^~~~
foo.cc:32:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   32 |  scanf("%d%d%d",&n,&m,&k);
      |  ~~~~~^~~~~~~~~~~~~~~~~~~
foo.cc:35:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   35 |   scanf("%d%d%d",&a[i].u,&a[i].v,&a[i].val);
      |   ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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