N = int(input())
A = list(map(int,input().split()))
B = [0]*N
B[0] = A[0]-A[1]
for i in range(1,N):
    B[i] = B[i-1]+A[2*i]-A[2*i+1]
ans = max(-B[N-1],B[N-1])
for i in range(N):
    cnt = 2*B[i-1]-B[N-1]
    ans = max(ans,cnt)
print(ans)