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

if n == 1:
    print(sushi_plates.pop())
    exit()

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

print(dp[n])