import math

N = input()
A = map(int, raw_input().strip().split()) + [0] * 100
K = int(math.sqrt(sum(A))) - 1


def height(k):
    if k < K + 1:
        return k + 1
    else:
        return 2 * K + 1 - k

pyramid = [height(i) for i in range(2 * K + 1)]
fixed = 0
for i in range(len(A) - len(pyramid)):
    fixed = max(fixed, sum(min(A[i+j], pyramid[j])
                           for j in range(len(pyramid))))
print(sum(A) - fixed)