import java.util.*

fun main(args: Array<String>) {
    val argList = Scanner(System.`in`)

    val n = argList.nextInt()
    val d = argList.nextInt()

    val e = GoldenApple()
    println(e.execute(n, d))

}

class GoldenApple {
    fun execute(n: Int, d: Int): Int {
        var amount = 0

        var currentTreeAmount = n

        while (currentTreeAmount > 0) {
            amount++

            currentTreeAmount -= (d * 2 + 1)
        }

        return amount
    }
}