program main
  implicit none
  integer::N,M,X,Y
  integer::i,small,big,mirror
  read *,N,M
  read *,X,Y
  small=MIN(X,Y)
  big  =X+Y-small
  mirror = 2*(small/M-1)*M-small + 1

  if((MOD(big-small,2*M).eq.0).or. &
       (MOD(big-mirror,2*M).eq.0) ) then
     print '(a)', "YES"
  else
     print '(a)', "NO"
  end if
end program main