n = int(input())
value = [ int(v) for v in input().split() ]
max_value = [ 0 for i in range(n)]


for i in range(n):
    if i == 0:
        max_value[i] = value[0]
    elif i == 1:
        max_value[i] = max(value[0], value[1])
    else:
        max_value[i] = max(max_value[i-1], max_value[i-2] + value[i])

print(max_value[-1])