module subprogram
	implicit none
contains
subroutine heapsort(n,array)
  implicit none
  integer,intent(in) :: n
  integer,intent(inout) :: array(1:n)
  
  integer ::i,k,j,l
  double precision :: 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 heapsort

end module subprogram

program main
	use subprogram
	implicit none
    integer N, i, l
	integer(8) S
	integer, allocatable :: A(:)
	read(*, *) N
	allocate(A(1:N))
	read(*, *) A(1:N)
	do i = 1, N
		A(i) = A(i) - i
	end do
	call heapsort(N,A)
	if(mod(N, 2) == 0) then
		l = A(N/2)
		do i = 1, N
			A(i) = A(i) - l
		end do
		S = 0
		do i = 1, N
			S = S + abs(A(i))
		end do
		write(*, *) S
	else
		l = A((N+1)/2)
		do i = 1, N
			A(i) = A(i) - l
		end do
		S = 0
		do i = 1, N
			S = S + abs(A(i))
		end do
		write(*, *) S
	end if
end program main