import java.util.*

fun main(args: Array<String>) {
    val n = readLine()!!.toInt()
    val v = readLine()!!.split(" ").map { it.toInt() }

    val flag = arrayOfNulls<Int?>(n)

    val task = Stack<Int>()
    task.add(0)
    while (task.isNotEmpty()) {
        val current = task.pop()
        if(current == v.lastIndex) {
            flag[current] = v[current]
            continue
        }
        if(current == v.lastIndex - 1) {
            flag[current] = Math.max(v[current], v[current+1])
            continue
        }
        if(flag[current + 1] == null) {
            task.add(current)
            task.add(current + 1)
            continue
        }
        if(flag[current + 2] == null) {
            task.add(current)
            task.add(current + 2)
            continue
        }
        flag[current] = Math.max(flag[current+1]!!, flag[current+2]!! + v[current])
    }
    println(flag[0]!!)
}