n = int(input())
v = list(map(int, input().split()))
dp = [0] * (n + 1)
dp[0] = v[0]
try:
    dp[1] = max(v[0], v[1])
except:
    pass
for i in range(2, n):
    dp[i] = max(dp[i - 1], dp[i - 2] + v[i])
print(dp[n - 1])