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

dp = [0, 0]
dp2 = [0, 0]

for v in vs:
    dp2 = [0, 0]
    dp2[0] = max(dp[0], dp[1])
    dp2[1] = dp[0] + v
    dp = dp2

print(max(dp))