n = int(input())
s = [int(_) for _ in input().split()]
ans = 0
for i in range(n):
  left = 0
  right = min(i,n-i-1)+1
  while right > left+1:
    mid = (left+right)//2
    p = True
    for j in range(max(mid-10,0),mid+1):
      if s[i+mid]+s[i-mid] != s[i]*2:
        p = False
    if p:
      left = mid
    else:
      right = mid
  ans += left
for i in range(1,n):
  left = 1
  right = min(i,n-i)+1
  while right > left+1:
    mid = (left+right)//2
    p = True
    for j in range(max(mid-10,1),mid+1):
      if s[i-mid]+s[i+mid-1] != s[i-1] + s[i]:
        p = False
    if p:
      left = mid
    else:
      right = mid
  ans += left
print(ans+n)