n = int(input())
v = [int(s) for s in input().split()]

dp = [0] * n
dp[0] = v[0]
if n > 1:
    dp[1] = max(v[1], v[0])

for i in range(2, n):
    dp[i] = max(dp[i - 1], dp[i - 2] + v[i])

print(dp[n - 1])