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)

//

fun main() {
    abc179c()
}

fun abc179c() {
    val n = readLine()!!.toInt()
    val table = IntArray(n) { 1 }
    table[0] = 0
    for (a in 2 until n) {
        var b = 1
        while (a * b <= n - 1) {
            table[a * b] += 1
            b++
        }
    }
    println(table.sum())
}