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 C (GCC 9.2.1) (judge verdict: Accepted)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
#include <math.h>

int main(void){

    long long N, K;

    scanf("%lld%lld", &N, &K);

    long long ans = 0;

    if(K != 0){
    for(long long b = K + 1; b <= N; b++){
        if(N % b < K){
            ans += (N / b) * (b-K);
        }else{
            ans += (N / b) * (b-K) + (N % b - K + 1);
        }
    }
    }else{
        ans = N * N;
    }

    printf("%lld\n", ans);

    return 0;
}