import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################

# https://ikatakos.com/pot/programming_algorithm/string_search
# Sの各文字を中心とする回文の奇数長の最大長を返す,O(S)
# 各文字の間に$を挟むことで偶数長も検出可
def Manacher(s: str):
    n = len(s)
    radius = [0] * n
    i = j = 0
    while i < n:
        while i - j >= 0 and i + j < n and s[i - j] == s[i + j]:
            j += 1
        radius[i] = j
        k = 1
        while i - k >= 0 and i + k < n and k + radius[i - k] < j:
            radius[i + k] = radius[i - k]
            k += 1
        i += k
        j -= k
    return [(r * 2 - 1) // 2 for r in radius]

n = ni()
a = na()
b = [a[i+1] - a[i] for i in range(n-1)]
c = [-10 ** 9]
for i in range(n-1):
    c.append(b[i])
    c.append(-10 ** 9)

res = Manacher(c)
# print(b)
# print(res)
ans = n
for i in range(len(res)):
    ans += (res[i] + 1) // 2

print(ans)