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

fn main(){ 
    let (n,k) = (read::<i64>(),read::<i64>());
    let mut r=0;
    for b in 1..n+1{
        r += max(0,min(k,b)-1);
    }
    for q in 1..n+1{
        for b in 1..n/q+1{
            //println!("{},{}", q, b);
            r += min(min(k,b),n-q*b+1);
        }
    }
    println!("{}", n*n-r)
}
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin.bytes().map(|c| c.expect("Error") as char) 
        .skip_while(|c| c.is_whitespace()).take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("Error")
}