N=int(input())
A=list(map(int, input().split()))
B=[]
for i in range(N-1):
  B.append(A[i+1]-A[i])

def manacher(S):
    C = []
    for a in S:
        C.append(a)
        C.append(0)
    C.pop()
    L = len(C)
    R = [0]*L
    i = j = 0
    while i < L:
        while j <= i < L-j and C[i-j] == C[i+j]:
            j += 1
        R[i] = j
        k = 1
        while j-R[i-k] > k <= i < L-k:
            R[i+k] = R[i-k]
            k += 1
        i += k; j -= k

    for i in range(L):
        if i & 1 == R[i] & 1:
            R[i] -= 1
    return R
  
ans=N
B=manacher(B)
for i in range(len(B)):
  ans+=(B[i]+1)//2

print(ans)