n = int(input())
s = [int(_) for _ in input().split()]
sa = []
for i in range(n-1):
  sa.append(s[i+1]-s[i])
def manacher(s):
  i = 0
  j = 0
  na = len(s)
  m = [0]*na
  while i < na:
    while i-j >= 0 and i+j < na and s[i-j] == s[i+j]:
      j += 1
    m[i] = j
    k = 1;
    while i-k >= 0 and k+m[i-k] < j:
      m[i+k] = m[i-k]
      k += 1
    i += k
    j -= k
  return m
m = manacher(sa)
ans = sum(m)
new = []
for i in sa:
  new.append(i)
  new.append('%')
m = manacher(new)
for i in range(len(m)):
  if i % 2 == 1:
    ans += m[i]//2
print(ans+n)