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: Time Limit Exceeded)

use proconio::input;
#[allow(unused_imports)]
use proconio::marker::{Bytes, Chars};
#[allow(unused_imports)]
use std::cmp::{min, max};

fn main() {
	input! {
		n: usize,
		k: usize,
	}

	// aはK以上。
	// a<b なら 余りは必ずK以上
	// 探索の範囲は、
	// K <= a <= N
	// 1 <= b <= a
	// これに、N-aを足せばいい。

	if k == 0 {
		println!("{}", n*n);
		return;
	}

	let mut ans = 0usize;
	for a in k..=n {
		if a > k*2 {
			for b in k+1..=a-k {
				if a % b >= k {
					ans += 1;
				} 
			}
		}
		ans += n-a;
	}
	println!("{}", ans);
}