N = int(input())
A = list(map(int, input().split()))
B = [0] * (N + 1)
C = [0] * (N + 1)

for i in range(N):
    B[i + 1] = A[i * 2] - A[i * 2 + 1] + B[i]
    C[N - i - 1] = A[(N - i) * 2 - 1] - A[(N - i) * 2 - 2] + C[N - i]
ans = 0

for i in range(N + 1):
    ans = max(ans, B[i] + C[i])
print(ans)