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)

extern crate proconio;
use proconio::input;
use std::cmp;

fn count_mod_ge(n:i32, b:i32, k:i32) -> i64 {
  let r = n / b;
  let m = n % b;
  let c = r * (b - k) + cmp::max(m + 1 - k, 0);
  match k {
    0 => (c - 1) as i64,
    _ => c as i64,
  }
}

fn main(){
  input!{ N: i32, K:i32 }
  let ans : i64 = (K + 1 ..= N).into_iter().map(|b| count_mod_ge(N, b, K)).sum();
  println!("{}", ans);
}