import java.util.*

fun main(args: Array<String>) {
    val pw = java.io.PrintWriter(System.out)
    Problem.solve(Scanner(System.`in`), pw)
    pw.flush()
}

object Problem {
    fun solve(sc: Scanner, pw: java.io.PrintWriter) {
        val N = sc.next().toInt()
        val f = LongArray(N + 1) { 1 }
        for (i in 2..N) {
            var j = i
            while (j <= N) {
                f[j]++
                j += i
            }
        }

        var ans = 0L
        for (i in 1..N) {
            ans += f[i] * i
        }
        pw.println(ans)
    }
}
