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 Go (1.14.1) (judge verdict: Accepted)

package main

import (
	"fmt"
	"math"
)

func main() {
	var n float64
	fmt.Scan(&n)
	cnt := 0
	for c := float64(n - 1); c >= 1; c-- {
		max := math.Floor(math.Sqrt(n - c))
		for a := float64(1); a <= max; a++ {
			b := (n - c) / a
			if b == math.Floor(b) {
				if a != b {
					cnt += 2
				} else {
					cnt++
				}
			}
		}
	}
	fmt.Println(cnt)
}