n = int(input())
A = list(map(int, input().split()))
i = 1
tot = sum(A)
while i * i <= tot:
    i += 1
i -= 1
A += [0] * i
ans = 0
for j in range(i):
    ans += max(0, A[j] - (j + 1))
    
for j in range(i, 2 * i - 1):
    ans += max(0, A[j] - (2 * i - j - 1))
print(ans + sum(A[2*i-1:]))