import java.lang.Math.floor

//

fun main() {
    abc172d()
}

fun abc172d() {
    val n = readLine()!!.toLong()
    var count = 0L
    for (i in 1L..n) {
        val y = floor(n / i.toDouble()).toLong()
        count += y * (y + 1) * i / 2
    }
    println(count)
}