program linear_approximation
  implicit none
  integer :: n, a(200000) = 0, i
  read(*,*) n
  read(*,*) a(1:n)
  do i = 1, n
    a(i) = a(i)-i
  end do
  call quick_sort(a(1:n))
  if (mod(n,2) == 0) then
    write(*,'(i0)') min(sum(int(abs(a(1:n)-a(n/2)),8)),sum(int(abs(a(1:n)-a(n/2+1)),8)))
  else
    write(*,'(i0)') sum(int(abs(a(1:n)-a((n+1)/2)),8))
  end if
contains
  recursive subroutine quick_sort(a)
    integer, intent(inout) :: a(:)
    integer :: n, l, r, m
    integer :: p
    n = size(a)
    l = 1
    r = n
    m = (n+1)/2
    p = a(l)+a(m)+a(r)-max(a(l),a(m),a(r))-min(a(l),a(m),a(r))
    do
      do while (a(l) < p)
        l = l+1
      end do
      do while (a(r) > p)
        r = r-1
      end do
      if (l >= r) exit
      a(l) = xor(a(l),a(r))
      a(r) = xor(a(l),a(r))
      a(l) = xor(a(l),a(r))
      l = l+1
      r = r-1
    end do
    if (l-1 > 1) call quick_sort(a(1:l-1))
    if (n > r+1) call quick_sort(a(r+1:n))
  end
end program linear_approximation