N = int(input())
V = map(int,input().split())

if N < 2:
    print(V[0])
else:
    yummy = [0] * int(N/2)
    yummy[0] = max(V[0], V[1])
    j = 1
    for i in range(3, N, 2):
        yummy[j] = yummy[j-1] + max(V[i], V[i-1])
        j += 1
    j -= 1
    if N % 2 == 1:
        if V[N-2] < V[N-1]:
            yummy[j] = yummy[j-1] + V[N-1]

    print(yummy[j])