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)

use std::io;
use std::str::FromStr;
use std::cmp::max;

fn input_tuple() -> (i64, i64) {
    let mut line: String = String::new();
    io::stdin().read_line(&mut line);
    let vec: Vec<i64> = line.split_whitespace().map(|s| s.parse().unwrap()).collect();
    (vec[0], vec[1])
}

fn main() {
    let (n, k) = input_tuple();
    let mut count = 0;
    if k == 0 {
        println!("{}", n * n);
        return;
    }
    for i in k+1..(n+1) {
        // println!("i = {}: {}", i, n / i * (i - k) + max(n % i as i64 + 1 - k, 0));
        count += n / i * (i - k) + max(n % i as i64 + 1 - k, 0);
    }
    println!("{}", count);
}