/in/foo.cc: In function 'int main()':
/in/foo.cc:19:18: warning: unused variable 'sum' [-Wunused-variable]
  int k,n,L,w,o,r,sum=0,book=0;
                  ^~~
/in/foo.cc:19:24: warning: unused variable 'book' [-Wunused-variable]
  int k,n,L,w,o,r,sum=0,book=0;
                        ^~~~