/in/foo.cc: In function 'int erfen(int, int)':
/in/foo.cc:23:22: warning: unused variable 'ANS' [-Wunused-variable]
  int head=0,tail=ans,ANS=0;
                      ^~~
/in/foo.cc:34:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^