def main():

    n = int(input())
    sushi_plates = list(map(int,input().split()))

    if n == 1:
        print(sushi_plates.pop())
        exit()

    else:
        dp = [0] + (n + 1)
        dp[1] = sushi_plates[1]
        for i in range(2, n + 1):
            dp[i] = max(dp[i - 1], dp[i - 2] + sushi_plates[i - 1])

        print(dp[n])

if __name__ == '__main__':
    main()