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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;

const int N=1e5+10;
long long dp[N];

int main() {
    int n, k;
    cin >> n >> k;
    long long ans = n*n;
    if ( k>0 )
        for (int i=n; i>0; i--) {
            ans -= min(i,k)-1;
            int m=n/i;
            ans -= (m-1)*min(i,k);
            ans -= min(n-m*i+1, k);
        }
    cout << ans << '\n';
    return 0;
}