N = int(raw_input())

data = map(int, raw_input().split())

if N == 1:
    print data[0]
    exit()

dp = [0] * N

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

for i in xrange(2, N):
    dp[i] = max(dp[i - 2] + data[i], dp[i - 1])

print dp[-1]