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)

const main = stdin => {
  const input = stdin.trim().split('\n')
  const N = parseInt(input[0])
  let c = 0
  for (let i = N - 1; i >= 1; i--) {
    for (let j = 1; j < N - 1; j++) {
      if (i * j >= N) {
        break
      }
      c++
    }
  }
  console.log(c + 1);
}


// 標準入力
main(require("fs").readFileSync("/dev/stdin", "utf8"))