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 JavaScript (Node.js 12.16.1) (judge verdict: Time Limit Exceeded)

function Main(input) {
    input = input.trim();
    const n = parseInt(input, 10);

    // nからc引いた数の約数の数を調べればいいんじゃね!?

    let count = 0;
    for(let c = 1; c < n; c++) {
       const subNum = n - c;

       count += toDivisor(subNum);
    }

    console.log(count);
}

// 約数の数を求める関数
function toDivisor(num) {
    let count = 0;
    let double = 0;
    for(let i = 1; i**2 <= num; i++) {
        if(num % i != 0) continue;
        if(i**2 === num) double++;
        count++;
    }

    return count * 2 - double;
}
 
Main(require("fs").readFileSync("/dev/stdin", "utf8"));