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

if N <= 2:
    print(max(V))
    exit()

dp = [0] * N
dp[0] = V[0]
dp[1] = max(V[0], V[1])
for i in range(2, N):
    dp[i] = max(dp[i-1], dp[i-2] + V[i])
print(dp[N-1])