import copy

n = int(input())
k = [int(x) for x in input().split()]

def func(num,num_list):
    total = 0
    a = [0,0]
    if num == 1:
        total = num_list[0]
    elif num == 2:
        total = max(num_list[0],num_list[1])
    elif num == 0:
        total = 0
    else:
        for i in range(2):
            a[i] += num_list[i]
            num2 = num - (i+2)
            ls = copy.copy(num_list)
            for _ in range(i+2):
                ls.pop(0)
            a[i] += func(num2,ls)
        total = max(a[0],a[1])
    return total

print(func(n,k))