def one_str():
    return input()

def many_int():
    return list(map(int, input().split()))

input_count = 0
N = many_int()[0]
A = many_int()

dp = [0]*N

dp[0] = A[0]

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

print(dp[N-1])