import java.util.ArrayDeque
import kotlin.math.max

fun main() {
    val builder = StringBuilder()

    val n = readInputLine().toInt()

    val vArr = readInputLine().split(" ").map { it.toInt() }

    // [sushi][取った:1 取らない:0]
    val dp = Array(n) { IntArray(2) }

    dp[0][1] = vArr[0]

    for (i in 1 until n) {
        dp[i][0] = max(dp[i - 1][0], dp[i - 1][1])
        dp[i][1] = dp[i - 1][0] + vArr[i]
    }

    builder.appendln(max(dp[n - 1][0], dp[n - 1][1]))

    print(builder.toString())
}

fun readInputLine(): String {
    return readLine()!!
}