N = int(input())
V = [int(s) for s in input().split()]


dp = [[0 for _ in range(2)] for _ in range(N + 1)]

for i in range(1, N + 1):
    dp[i][0] = max(dp[i - 1][0], dp[i - 1][1])
    dp[i][1] = dp[i - 1][0] + V[i - 1]

answer = max(dp[N][0], dp[N][1])
print(answer)