import sys
input = sys.stdin.readline

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

if N==1:
    print(1)
    exit()

X=[]
for i in range(1,N):
    X.append(A[i]-A[i-1])
    X.append(-1)

X.pop()
S=X

LEN=len(S)
i=0
j=0
R=[0]*LEN # 文字 i を中心とする最長の回文の半径

while i<LEN:
    while i-j>=0 and i+j<LEN and S[i-j]==S[i+j]:
        j+=1
    R[i]=j
    
    k=1
    while i-k>=0 and i+k<LEN and k+R[i-k]<j:
        R[i+k]=R[i-k]
        k+=1

    i+=k
    j-=k

ANS=0
for i in range(len(X)):
    if i%2==1:
        ANS+=R[i]//2+1
    else:
        ANS+=(R[i]+1)//2

print(ANS+2)