N = int(input())
A = [0]*N + list(map(int, input().split())) + [0]*N
print(A)
# k 乗根
def sqrt(n: int, k = 2):
    l = k - 1
    if not n: return 0
    y = 1 << (n.bit_length() + l) // k
    x = y + 1
    while y < x:
        x = y
        y = (l * x + n // (x ** l)) // k
    return x

total = sum(A)
H = sqrt(total)

ans = total
for h in range(1, H + 1): # ピラミッドの高さを固定
    for l in range(3*N): # 開始地点（左端）を固定
        if l + 2*h - 2 >= 3*N:
            break
        model = 1
        sign = 1
        no_need_to_move = 0
        for i in range(2*h - 2 + 1):

            cur = A[l + i]
            no_need_to_move += min(cur, model)

            if model == h: # 真ん中に到達
                sign *= -1

            model += sign
        score = total - no_need_to_move
        ans = min(ans, score)
print(ans)