implicit none
  integer::N,i,temp
  integer::V(1000),first,p,pp,tmp
  read *, N
  read *, V(1:N)

  pp=0
  p =V(1)
  do i=2,N
     tmp = p
     p   = MAX(p,pp+V(i))
     pp  = tmp
  end do
  print '(i0)',p
end