/in/foo.cc: In function 'int main()':
/in/foo.cc:18:6: warning: unused variable 'l1' [-Wunused-variable]
  int l1=n,l2=0;
      ^~
/in/foo.cc:18:11: warning: unused variable 'l2' [-Wunused-variable]
  int l1=n,l2=0;
           ^~
/in/foo.cc:21:6: warning: unused variable 'head' [-Wunused-variable]
  int head=1;
      ^~~~