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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long n = sc.nextLong();
        int k = sc.nextInt();
        long ans = 0;

        for (int i = 1; i <= n; i++) {
            // bの値を動かす
            if (i - 1 < k) {
                continue;
            }
            long setCount = n / i;
            int canUse = i - k;
            ans += setCount * canUse;
            if (n % i - k >= 0) {
                ans += (n % i) - k + 1;
            }
        }
        if (k == 0) {
            ans = n * n;
        }
        System.out.println(ans);
        sc.close();
    }
}