/in/foo.cc: In function 'int main()':
/in/foo.cc:6:8: warning: unused variable 'k' [-Wunused-variable]
  int n,k,sum;
        ^
/in/foo.cc:15:11: warning: 'sum' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<sum;
           ^