fun main() {
    val N: Int = readLine()!!.toInt()
    var V: IntArray = readLine()!!.split(" ").map(String::toInt).toIntArray()

    fun getPlusValue(targetIndex: Int): Int {
        return if (targetIndex < V.size) V[targetIndex] else 0
    }

    for (i in (V.size - 1 downTo 0)) {
        val plus2 = getPlusValue(i + 2)
        val plus3 = getPlusValue(i + 3)
        V[i] += if (plus2 > plus3) plus2 else plus3
    }
    println(V.max())
}