foo.cc: In function 'int main()':
foo.cc:9:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    9 |     scanf("%d%d", &n, &k);//输入
      |     ~~~~~^~~~~~~~~~~~~~~~
foo.cc:13:18: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   13 |             scanf("%d", &a);
      |             ~~~~~^~~~~~~~~~

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