N = int(input())
value_list = map(int, input.split(' '))

dp = [[0, 0] for _ in range(1001)]
dp[0][0] = 0
dp[0][1] = value_list[0]
dp[1][0] = value_list[0]
dp[1][1] = value_list[1]

for i in range(2, N):
    dp[i][0] = max(dp[i-1][1], dp[i-2][1])
    dp[i][1] = max(dp[i-1][0] + value_list[i], dp[i-2][0] + value_list[i])
ans = max(dp[N-1][0], dp[N-1][1])
print(ans)