foo.cc: In function 'int main()':
foo.cc:109:22: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long long int' [-Wformat=]
     printf("%d\n",ans);
                      ^
foo.cc:91:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d",&n,&k);
  ~~~~~^~~~~~~~~~~~~~
foo.cc:93:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&a[i]);
     ~~~~~^~~~~~~~~~~~

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