Problem:
Score : 400 points

Problem Statement

Takahashi had a pair of two positive integers not exceeding N, (a,b), which he has forgotten.
He remembers that the remainder of a divided by b was greater than or equal to K.
Find the number of possible pairs that he may have had.

Constraints

1 \leq N \leq 10^5

0 \leq K \leq N-1

All input values are integers.

Input

Input is given from Standard Input in the following format:

N K

Output

Print the number of possible pairs that he may have had.

Sample Input 1

5 2

Sample Output 1

7

There are seven possible pairs: (2,3),(5,3),(2,4),(3,4),(2,5),(3,5) and (4,5).

Sample Input 2

10 0

Sample Output 2

100

Sample Input 3

31415 9265

Sample Output 3

287927211

Solution in Rust (1.42.0) (judge verdict: Accepted)

#![allow(unused_imports)]
use proconio::input;
use proconio::marker::*;
use std::collections::VecDeque;

fn main() {
  input!{
    n: usize,
    k: usize
  }
  
  let mut result = 0;
  for b in 1..=n {
    let v = if b < k {
      0
    } else {
      b - k
    };
    let p = n % b;
    let pv = if p + 1 < k {
      0
    } else {
      p - k + 1
    };

    let m = n / b;
    let v = m * v + pv;
    result += v;
  }
  
  if k == 0 {
    result -= n;
  }
  
  println!("{}", result);
}