N = int(input())
v = [int(i) for i in input().split()]

dp = [0 for i in range(N)] # DPテーブルの作成

if N == 1:
    dp[0] = v[0]
else:
    dp[0] = v[0]
    dp[1] = max(dp[0], v[1])
    for k in range(2,N):
        dp[k] = max(dp[k-1], dp[k-2]+v[k])
print(dp[N-1])