n = int(input())
lst1 = list(map(int,input().split()))

dp = [0]*n

dp[0] = lst1[0]
dp[1] = max(lst1[0],lst1[1])

for i in range(1,n):
    dp[i] = max(dp[i-1],dp[i-2]+lst1[i])

print(dp[-1])