n = int(input())
list_n = [int(i) for i in input().split()]
dp = [0] * n
for i in range(n):
    if i <= 1:
        dp[i] = max(list_n[:i+1])
    else:
        dp[i] = max(dp[i-2]+list_n[i], dp[i-1])
print(max(dp))