def calc_move(As, size):
    pyramid = [i for i in range(1, size + 1)] + [i for i in range(size - 1, 0, -1)]
    plus = 0
    minus = 0
    for a, p in zip(As, pyramid):
        if a > p:
            plus += a - p
        elif a < p:
            minus += p - a
    if len(As) > len(pyramid):
        plus += sum(As[len(pyramid):])
    if len(As) < len(pyramid):
        minus += sum(pyramid[len(As):])
    return max(plus, minus)

N = int(input())
As = list(map(int, input().split()))

min_move = sum(As) - 1
max_size = int(sum(As)**0.5)
for size in range(2, max_size + 1):
    move = calc_move(As, size)
    if move < min_move:
        min_move = move
print(min_move)