fun main() {
    val N: Int = readLine()!!.toInt()
    val V: List<Int> = readLine()!!.split(" ").map(String::toInt)

    fun getMaxOishisa(i: Int): Int {
        if (i >= V.size) {
            return 0
        }
        val currentOishisa = if (i < 0) 0 else V[i]
        val oishisa1 = getMaxOishisa(i + 2)
        val oishisa2 = getMaxOishisa(i + 3)
        return when (oishisa1 > oishisa2) {
            true -> oishisa1 + currentOishisa
            false -> oishisa2 + currentOishisa
        }
    }

    println(getMaxOishisa(-2))
}