N = int(intput())
V = list(map(int, input().split()))
DP = [0] * N

for i in range(N):
    if i == 0:
        DP[0] = V[0]
    elif i == 1:
        DP[1] = max(DP[i-1], V[1])
    else:
        DP[i] = max(DP[i-1], DP[i-2] + V[i])

print(DP[N-1])