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


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

if N == 3:
    exit(print(min(V[0] + V[2], V[1])))

dp = [0]*N
dp[0] = V[0]
dp[1] = V[1]

for i in range(3, N):
    dp[i] = max(dp[i - 2], dp[i - 3]) + V[i]

print(max(dp))