fun main() = Thread(null, ::abc172d, "(^o^)", 128 * 1024 * 1024).apply { start() }.join()

@OptIn(ExperimentalStdlibApi::class)
fun abc172d() {
    val k = readLine()!!.toLong()

    var answer = 0L

    for (n in 1..k) for (m in n..k step n) {
        answer += m
    }

    println(answer)
}
