n = input()
a = map(int, raw_input().split())
total = sum(a)

h = 1
ans = float('inf')
while h * h <= total:
	w = h * 2 - 1
	for j in xrange(n):
		low = 0
		high = 0
		for i in xrange(-111, 111):
			y = max(0, (i - j) + h if i <= j else -(i - j) + h)
			if 0 <= i and i < n:
				if a[i] < y:
					low += y - a[i]
				elif a[i] > y:
					high += a[i] - y
			else:
				high += y
		ans = min(ans, max(low, high))
	h += 1

print ans