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: Time Limit Exceeded)

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strconv"
)

// const abcd = "abcdefghijklmnopqrstuvwxyz"
// const ABCD = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
// var dx = [...]int{0, 1, 0, -1, 1, -1, -1, 1}
// var dy = [...]int{1, 0, -1, 0, 1, 1, -1, -1}
// var inf int = 1e13

// var mod = 1000000007
var next = newScanner()

// ---------------------------------------------------------

func main() {
	log.SetFlags(log.Lshortfile)
	N := next.Int()
	K := next.Int()
	ans := 0
	for i := K; i <= N; i++ {
		// cnt := 0
		// for j := K; j <= i; j++ {
		// 	if j%i >= K {
		// 		cnt++
		// 		// log.Println(j, i, "●", cnt)
		// 	} else {
		// 		// log.Println(j, i, "✕")
		// 	}
		// }
		cnt := i - K
		// log.Println(i, cnt, i-K)
		if i != 0 {
			cnt *= (N / i)

			for j := i*(N/i) + 1; j <= N; j++ {
				if j%i >= K {
					cnt++
				}
			}
		}
		ans += cnt
	}
	fmt.Println(ans)
}

// ---------------------------------------------------------

// Pair is...
type Pair struct {
	a, b int
}

// Pairs is sorted by []Pair struct
type Pairs []Pair

func (p Pairs) Len() int {
	return len(p)
}
func (p Pairs) Swap(i, j int) {
	p[i], p[j] = p[j], p[i]
}

func (p Pairs) Less(i, j int) bool {
	return p[i].b < p[i].b
}

// func (p Pairs) Less(i, j int) bool {
// 	if p[i].a < p[j].a {
// 		return true
// 	} else if p[i].a == p[j].a {
// 		return p[i].b < p[j].b
// 	}
// 	return false
// }

// ------int method-------------------------
func in(c, a, z int) bool {
	return c >= a && c < z
}
func out(c, a, z int) bool {
	return !in(c, a, z)
}
func btoi(b bool) int {
	if b {
		return 1
	}
	return 0
}
func itob(a int) bool {
	if a == 0 {
		return false
	}
	return true
}
func max(a ...int) int {
	r := a[0]
	for i := 0; i < len(a); i++ {
		if r < a[i] {
			r = a[i]
		}
	}
	return r
}
func min(a ...int) int {
	r := a[0]
	for i := 0; i < len(a); i++ {
		if r > a[i] {
			r = a[i]
		}
	}
	return r
}
func sum(a []int) int {
	r := 0
	for i := 0; i < len(a); i++ {
		r += a[i]
	}
	return r
}
func pro(a []int) int {
	r := 1
	for i := 0; i < len(a); i++ {
		r *= a[i]
	}
	return r
}
func fill(a []int, n int) []int {
	for i := 0; i < len(a); i++ {
		a[i] = n
	}
	return a
}
func minmax(a, b int) (int, int) {
	if a > b {
		return b, a
	}
	return a, b
}
func abs(a int) int {
	if a < 0 {
		return -a
	}
	return a
}
func ceil(a, b int) int {
	if a%b != 0 {
		return 1
	}
	return 0
}

// ---------- buffered scanner -----------------------------------------
type scanner struct {
	r   *bufio.Reader
	buf []byte
	p   int
}

func newScanner() *scanner {
	rdr := bufio.NewReaderSize(os.Stdin, 10000)
	return &scanner{r: rdr}
}
func (s *scanner) next() string {
	s.pre()
	start := s.p
	for ; s.p < len(s.buf); s.p++ {
		if s.buf[s.p] == ' ' {
			break
		}
	}
	result := string(s.buf[start:s.p])
	s.p++
	return result
}
func (s *scanner) Line() string {
	s.pre()
	start := s.p
	s.p = len(s.buf)
	return string(s.buf[start:])
}
func (s *scanner) String() string {
	return s.next()
}
func (s *scanner) Int() int {
	v, err := strconv.Atoi(s.next())
	if err != nil {
		log.Fatal(err)
	}
	return v
}
func (s *scanner) Ints(n int) []int {
	r := make([]int, n)
	for i := 0; i < n; i++ {
		r[i] = s.Int()
	}
	return r
}
func (s *scanner) Int64() int64 {
	v, err := strconv.ParseInt(s.next(), 10, 64)
	if err != nil {
		log.Fatal(err)
	}
	return v
}
func (s *scanner) Uint64() uint64 {
	v, err := strconv.ParseUint(s.next(), 10, 64)
	if err != nil {
		log.Fatal(err)
	}
	return v
}
func (s *scanner) Float64() float64 {
	v, err := strconv.ParseFloat(s.next(), 64)
	if err != nil {
		log.Fatal(err)
	}
	return v
}
func (s *scanner) pre() {
	if s.p >= len(s.buf) {
		s.readLine()
		s.p = 0
	}
}
func (s *scanner) readLine() {
	s.buf = make([]byte, 0)
	for {
		l, p, err := s.r.ReadLine()
		if err != nil {
			log.Fatal(err)
		}
		s.buf = append(s.buf, l...)
		if !p {
			break
		}
	}
}