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

h = 1
ans = float('inf')
while h * h <= total:
	c = h - 1
	low = 0
	high = 0
	for i in xrange(1000):
		y = max(0, (i - c) + h if i <= c else -(i - c) + h)
		if 0 <= i and i < n:
			if a[i] < y:
				low += y - a[i]
			elif a[i] > y:
				high += a[i] - y
		else:
			low += y
	ans = min(ans, max(low, high))
	h += 1

print ans