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 (1.15.1) (judge verdict: Accepted)

use std::io;
use std::io::Read;

fn main () {
    let mut lines = String::new();
    io::stdin().read_to_string(&mut lines).unwrap();

    let mut results = String::new();
    for line in lines.split('\n') {
        if line == "" {
            break;
        }
        let mut line_iter = line.split_whitespace();
        let n: i64 = line_iter.next().unwrap().parse().unwrap();
        let k: i64 = line_iter.next().unwrap().parse().unwrap();

        let mut count: i64 = 0;
        if k == 0 {
            count = n * n;
        } else {
            let min = k + 1;
            for b in min..(n+1) {
                count += (n/b) * (b-k);
                if (n%b) - k >= 0 {
                    count += (n%b) - k + 1;
                }
            }
        }
        results += &format!("{}\n", count);
    }
    println!("{}", results);
}