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>
#define _CRT_SECURE_NO_WARNINGS
#define ll long long
#define BUF 50
using namespace std;
ll MOD = 1e9 + 7;
ll A, B, C, D, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
string S;
ll ans = 0;

int main() {
	cin >> N >> K;
	for (int b = K + 1; b <= N; b++) {
		int x = (N - K) / b;
		if (x == 0&&b-1<=N)ans += b - K;
		else ans += (b - K)*x + (N - (x*b + K) + 1);
	}
	cout << ans << endl;
}