foo.cc: In function 'int main()':
foo.cc:13:25: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     int n,k,cnt=0; scanf("%d%d",&n,&k);
                    ~~~~~^~~~~~~~~~~~~~
foo.cc:15:31: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     for(int i=0;i<n;i++) scanf("%d",&a[i]);
                          ~~~~~^~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。