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 kotlin.math.sqrt

fun main(args: Array<String>) {
  val n: Int = readLine()!!.toInt()
  val memo: MutableList<Int> = mutableListOf()
  for (i in 1..n - 1) {
    memo.add(calc(i))
  }
  println(memo.sum())
}

fun calc(i: Int): Int {
  var answer = 0
  val n = sqrt(i.toDouble()).toInt()

  for (j in 1..n) {
    if (i % j == 0) {
      answer += 1
    }
  }
  if (i == n * n) {
    answer = answer * 2 - 1
  } else {
    answer = answer * 2
  }
  return answer
}