def Manacher(S):
    C = [-1]
    for s in S:
        C.append(s)
        C.append(-1)
    R = [0]*len(C)
    i = 0
    j = 0
    while i < len(C):
        SUM = -1
        if i%2 == 0:
            if 1 <= i and i+1 < len(C):
                SUM = C[i-1]+C[i+1]
        else:
            SUM = C[i]*2
        while 0 <= i-j and i+j < len(C) and (C[i-j]+C[i+j] == SUM or C[i-j] == -1):
            j += 1
        R[i] = j
        k = 1
        while 0 <= i-k and k+R[i-k] < j:
            R[i+k] = R[i-k]
            k += 1
        i += k
        j -= k
    odd = []
    even = []
    for i in range(1, len(C)-1):
        if i%2 == 1:
            odd.append(R[i]//2)
        else:
            even.append(R[i]//2)
    return odd, even

N = int(input())
A = list(map(int, input().split()))

odd, even = Manacher(A)
ans = 0
for o in odd:
    ans += o
for e in even:
    ans += e

print(ans)