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: Accepted)

let inputString = "";
let currentLine = 0;
process.stdin.on("data", (data) => {
  inputString += data;
});
process.stdin.on("end", function () {
  inputString = inputString
    .trim()
    .split("\n")
    .map((str) => str.trim());
  main();
});
function readLine() {
  return inputString[currentLine++];
}

// utils
const MOD = 1e9 + 7;
const mod = (n) => ((n % MOD) + MOD) % MOD;
const add = (a, b) => mod(mod(a) + mod(b));
const sub = (a, b) => mod(mod(a) - mod(b));
function mul() {
  for (var a = arguments, r = a[0], i = a.length; --i; )
    r = ((((r >> 16) * a[i]) % MOD) * 65536 + (r & 65535) * a[i]) % MOD;
  return r;
}
function inv(b) {
  for (var a = MOD, u = 0, v = 1, t; b; v = t)
    (t = (a / b) | 0), (a -= t * b), (u -= t * v), (t = a), (a = b), (b = t), (t = u), (u = v);
  u %= MOD;
  return u < 0 ? u + MOD : u;
}
function pow(base, n) {
  if (n === 0) return 1;
  let p = pow(base, Math.floor(n / 2));
  let res = mul(mod(p), mod(p));
  if (n % 2 === 1) res = mul(mod(res), base);
  return res;
}

function main() {
  const n = +readLine();
  let ans = 0;

  for (let i = 1; i <= n; i++) {
    ans += Math.floor((n - 1) / i);
  }

  console.log(ans);
}