N = int(input())
A = list(map(int,input().split()))
B = [A[i]-A[i-1] for i in range(1,N)]
d = [0]*(N-1)
l = 0
r = -1
ans = 0
for i in range(N-1):
    if i>r:
        k = 1
    else:
        k = min(d[r+l-i],r-i+1)
    while i-k>=0 and i+k<N-1:
        if B[i-k]==B[i+k]:
            k += 1
        else:break
    d[i] = k
    ans += k
    if i+k-1>r:
        r = i+k-1
        l = i-k+1
l = 0
r = -1
for i in range(1,N-1):
    if i>r:
        k = 0
    else:
        k = min(d[r+1+l-i],r-i+1)
    while i-k-1>=0 and i+k<N-1:
        if B[i-k-1]==B[i+k]:
            k += 1
        else:break
    d[i] = k
    ans += k
    if i+k-1>r:
        r = i+k-1
        l = i-k
print(ans+N)