foo.cc: In function 'bool check(int)':
foo.cc:81:6: warning: unused variable 'flow' [-Wunused-variable]
   81 |  int flow=0;
      |      ^~~~
foo.cc: In function 'int main()':
foo.cc:92:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   92 |  scanf("%d%d",&n,&k);
      |  ~~~~~^~~~~~~~~~~~~~

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