PROGRAM ATCODER

implicit none
integer(16) :: n,i,ans
integer(16),allocatable :: a(:)

read*, n
allocate(a(n))
read*, a(1:n)

call hs(n,a)

do i = n-1, 0, -2
  if ( i == 0 ) then
    if ( a(1) /= 0 ) then
      print'(i0)', 0
      stop
    end if
    exit
  end if
  if ( 2*i /= a(i)+a(i+1) ) then
    print'(i0)', 0
    stop
  end if
end do

ans = 1
do i = 1, n/2
  ans = mod(ans*2,10**9+7)
end do

print'(i0)', ans 

contains
!!!!!! サブルーチンは↓
subroutine hs(n,array)
  implicit none
  integer(16),intent(in)::n
  integer(16),intent(inout)::array(1:n)
  
  integer(16)::i,k,j,l,m
  integer(16)::t
  
  if(n.le.0)then
     write(6,*)"Error, at heapsort"; stop
  endif
  if(n.eq.1)return
 
  l=n/2+1
  k=n
  do while(k.ne.1)
     if(l.gt.1)then
        l=l-1
        t=array(l)
     else
        t=array(k)
        array(k)=array(1)
        k=k-1
        if(k.eq.1) then
           array(1)=t
           exit
        endif
     endif
     i=l
     j=l+l
     do while(j.le.k)
        if(j.lt.k)then
           if(array(j).lt.array(j+1))j=j+1
        endif
        if (t.lt.array(j))then
           array(i)=array(j)
           i=j
           j=j+j
        else
           j=k+1
        endif
     enddo
     array(i)=t
  enddo
 
  return
end subroutine hs
!!!!!!

END PROGRAM ATCODER