from math import sqrt

N = int(input())
blocks = [int(i) for i in input().split()]
total = sum(blocks)
n = int(sqrt(total))

plus = 0
for i in range(n):
    if i < N:
        plus += max(blocks[i] - (i + 1), 0)
for i in range(n, 2*n-1):
    if i < N:
        plus += max(blocks[i] - (2*n-1 - i), 0)
# 作るピラミッド列よりも与えられたブロック数が多い場合
if 2*n-1 <= N:
    for i in range(2*n-1, N):
        plus += blocks[i]

print(plus)