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

if n == 1:
    print(v[0])
else:
    a = [0] * (n+1)
    a[1] = v[0]
    for i in range(2, n+1):
        a[i] = max(a[i-1], v[i-1] + a[i-2])

    print(a[n])