n = int(input())
A = list(map(int, input().split()))

sumA = sum(A)
h = 0
while (h + 1)**2 <= sumA:
    h += 1
ans = 0
for i in range(n):
    if i < h:
        ans += max(A[i] - (i + 1), 0)
    else:
        ans += max(A[i] - max(0, 2 * h - i - 1), 0)
print(ans)