program test
integer(8) :: nn,k,a(100),b(100),i,a_min,nk(0:10000),atai,sig


read(*,*) nn,k
read(*,*) (a(i),i=1,nn)

do i = 1,nn
	b(i) = i
enddo

call heapsort2(nn,a(1:nn),b(1:nn))

atai = nn
sig = -1
do i=1,10000
	nk(i) = b(atai)
	atai = atai + sig
	if(atai == 1) then
		sig = 1
	else if (atai == nn) then
		sig = -1
	endif
	
enddo

if(a(1) <= k-1 .or. a(2) <= k) then
	write(*,*) -1
else
	write(*,*) nn + (nn-1)*k
	write(*,*) (nk(i),i=1,nn + (nn-1)*k)
endif

contains
 
subroutine heapsort2(n,y1,y2)
 
	implicit none
	integer(8),intent(in) :: n
	integer(8),intent(inout) :: y1(1:n)
	integer(8),intent(inout) :: y2(1:n)
	integer(8) :: i,k,j,l
	integer(8) :: t1,t2
	
	l = n/2+1
	k = n
 
	do while (k /= 1)
		 if(l > 1) then
				l = l-1
				t1 = y1(l)
				t2 = y2(l)
				
		 else
				t1 = y1(k)
				t2 = y2(k)
				y1(k) = y1(1)
				y2(k) = y2(1)
				k = k-1
				if(k == 1) then
					 y1(1) = t1
					 y2(1) = t2
					 exit
				endif
		 endif
 
		 i = l
		 j = l+l
 
		 do while(j <= k)
				if(j < k) then
					 if(y1(j) < y1(j+1)) j = j+1
				endif
				
				if (t1 < y1(j)) then
					 y1(i) = y1(j)
					 y2(i) = y2(j)
					 i = j
					 j = j+j
				else
					 j = k+1
				endif
		 
		 enddo
		 
		 y1(i) = t1
		 y2(i) = t2
	
	enddo
	return
 
end subroutine heapsort2

end program