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

if n == 1:
    print(V[0])
    exit()

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

print(max(dp))