fun main(arr:Array<String>) {
    val ballCount = readLine()!!.toLong()
    var max = 0.toLong()
    for(i in (2..ballCount)) {
        if(i > ballCount) {
            break
        }
        var big = ballCount - (i - 1)
        val ans = big * i + (ballCount - big)
        max = Math.max(max, ans)
    }
    println(max)
}