fun main(args: Array<String>) {
    val n = getInt()
    val a = LongArray(n + 1)
    var out = 0L

    (1..n).forEach { k ->
        var i = k
        while (i <= n) {
            a[i]++
            i += k
        }

        out += k * a[k]
    }
    println(out)
}

fun getInt() = readLine()!!.toInt()