N = int(input())
A = list(map(int, input().split()))
s = sum(A)

ans = 100*100+10
max_height = int(s**0.5)
max_bottom = 2* max_height - 1
for bottom in range(1, max_bottom+1, 2):
    plus = 0
    for i in range(max(N, bottom)):
        if i < bottom:
            h = bottom -i if i > bottom // 2 else i + 1
        else:
            h = 0
        if i < N and A[i] > h:
            plus += A[i] - h
    ans = min(ans, plus)
print(ans)