Problem:
Score : 300 points

Problem Statement

Given is a positive integer N.
How many tuples (A,B,C) of positive integers satisfy A \times B + C = N?

Constraints

2 \leq N \leq 10^6

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer.

Sample Input 1

3

Sample Output 1

3

There are 3 tuples of integers that satisfy A \times B + C = 3: (A, B, C) = (1, 1, 2), (1, 2, 1), (2, 1, 1).

Sample Input 2

100

Sample Output 2

473

Sample Input 3

1000000

Sample Output 3

13969985

Solution in Kotlin (1.3.71) (judge verdict: Accepted)

import java.util.*
import kotlin.math.*

fun str() = readLine()!!
fun int() = str().toInt()
fun long() = str().toLong()

fun read(d: String = " ") = str().split(d)
fun <T> list(d: String = " ", f: String.() -> T) = read(d).map { f(it) }
fun list() = list { toInt() }

fun <T> MutableList<T>.removeLast() = this.removeAt(this.lastIndex)

const val mod = 1000000007L

fun main() {
    abc000X()
}

fun abc000X() {
    val n = int()
    (1..n).map { (n - 1L) / it }.sum().let { println(it) }
}