foo.cc: In function 'int main()':
foo.cc:5:10: warning: unused variable 'k' [-Wunused-variable]
    5 |  int n,m,k,sum=0;
      |          ^
foo.cc:6:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    6 |  scanf("%d%d",&n,&m);
      |  ~~~~~^~~~~~~~~~~~~~
foo.cc:8:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    8 |   scanf("%d",&a[i]);
      |   ~~~~~^~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务