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"

func main(){
  var N,K int
  fmt.Scan(&N,&K)
  //K以上のbに対して、あまりがK以上になるaがいくつあるか
  //c := N/b cb <= N < (c+1)b
  //c(b-K) + (N-cb)-K if N-cb >= K else 0
  result := 0
  for b := K+1; b<=N; b++{
    c := N/b
    d := 0

    if (N - c*b) >= K && K==0{
      d = (N- c*b) - K
    }else if (N - c*b) >= K{
      d = (N- c*b) -K +1
    }else{
      d = 0
    }
    // fmt.Println(b,c,d, c*(b-K) + d)
    result += c*(b-K) + d
  }
  fmt.Println(result)
}