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++ (Clang 10.0.0) (judge verdict: Wrong Answer)

#include <iostream>
using namespace std;
#define ll long long
#define all(x) x.begin(),x.end() 

int const N = 200001;
//245322325‬

int main(){
    #ifndef ONLINE_JUDGE
    freopen("read.txt","r",stdin);
    #endif
    int n, k;
    scanf("%d%d", &n, &k);
    ll an = 1ll * (n-k) * (n-k+1) >> 1;
    for(int i = k+1; i<=n; ++i){
        int x = max(0, (i-k)-(i/2));
        an += x;
    }
    printf("%lld\n", !k? 1ll * n * n: an);
}