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 Go (1.6) (judge verdict: Accepted)

package main

import "fmt"

// 2018-08-04T13:47:11+0800
// 2018-08-04T14:03:18+0800
// 2018-08-04T14:40:46+0800
func main() {
	var N, K int
	fmt.Scanf("%d%d", &N, &K)
	out := 0
	for b := K + 1; b <= N; b++ {
		span := b - K
		mul := (N - K) / b
		if mul == 0 {
			out += span
		} else {
			out += span * mul
			if mul*b+b <= N {
				out += span
			} else {
				out += N + 1 - (mul*b + K)
			}
		}
	}
	if K == 0 {
		out -= N - K
	}
	fmt.Println(out)
}