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

cuml = [0]
cumr = [0]

for i in range(N):
    cuml.append(cuml[-1] + A[2 * i] - A[2 * i + 1])
    cumr.append(cumr[-1] + A[-2 * i - 1] - A[-2 * i - 2])

ans = -10**18

for i in range(N + 1):
    ans = max(ans, cuml[i] + cumr[- i - 1])

print(ans)