题解 | 宵暗的妖怪

fmin = lambda x, y: x if x < y else y
fmax = lambda x, y: x if x > y else y

# @TIME
def solve(testcase):
    n = II()
    A = LII()

    dp = [0 for _ in range(n + 1)]

    for i, v in enumerate(A, 1):
        dp[i] = dp[i - 1]
        if i >= 3:
            dp[i] = fmax(dp[i], dp[i - 3] + A[i - 2])
    
    print(dp[n])

for testcase in range(1):
    solve(testcase)