implicit none
  integer::N,M,X,Y
  read *, N,M
  read *, X,Y
  X = MOD((X-1),2*M)
  Y = MOD((Y-1),2*M)
  if(X.ge.M) then
     X = 2*M-X -1
  end if
  if(Y.ge.M) then
     Y = 2*M-Y -1
  end if

  if(X.eq.Y) then
     print '(a)', "YES"
  else
     print '(a)', "NO"
  end if
end program