N, *A = map(int, open(0).read().split())

x = list(range(1, N // 2 + 1)) + [(N + 1) // 2] + list(range(N // 2, 1 - 1, -1))

a = 0
b = 0
for i in range(N):
    t = A[i] - x[i]
    if t < 0:
        a += -t
    elif t > 0:
        b += t
print(b)