n = int(input())
a = list(map(int, input().split()))
r = [0]
l = [0]
total = 0
for i in range(n):
    total += a[2 * i] - a[2 * i + 1]
    l.append(total)
total = 0
for i in range(n - 1, -1, -1):
    total += a[2 * i + 1] - a[2 * i]
    r.append(total)

ans = -10 ** 10
for rr, ll in zip(r, l[::-1]):
    ans = max(ans, rr + ll)
print(ans)