N = int(input())
l = list(map(int, input().split()))
zero_l = [0 for i in range(120)]
l = l + zero_l 
sum = 0

for l_i in l:
    sum += int(l_i)

top = 0
while sum >= top * top:
    top += 1 

top -= 1
copy_top = top - 1
pyramid = []

for i in range(1, top + 1):
    pyramid.append(i)

for i in range(len(pyramid) - 1):
    pyramid.append(copy_top)
    copy_top -= 1
pyramid = pyramid + [0]
ans = 0

for i in range(len(l) - len(pyramid)):
    ck_here = i
    ck_ans = 0
    for j in range(len(pyramid)):
        ck_ans += min(l[ck_here], pyramid[j])
        ck_here += 1
    if ck_ans > ans:
        ans = ck_ans
    

print(sum - ans)