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 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
int main(void){
int n,k,i,p,q;
int cnt = 0;
scanf("%d%d", &n,&k);
if(k ==0){
cnt += ((n - 1) * n + n);
}
else {
cnt += ((n - k) * (n - k +1) / 2);
for(i = k + 1;i <= n;i++){
p = (n - (i - 1)) / i;
q = (n - (i - 1)) % i;
cnt += ((i - k) * p);
cnt += ((q > k) ? (q - k) : 0); 
}
}
printf("%d",cnt);
return 0;
}