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: Accepted)

#include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
#include<map>
#include<set>
#include<stack>
#include<cmath>
#include<sstream>
#include<string>
#include<numeric>
using namespace std;
typedef long long ll;
//ll mod = 1e9+7;
ll mod = 998244353;
#define rep(i,n) for(int i = 0; i < (n); ++i)

int main(){
    ll n, k;
    cin >> n >> k;
    ll ans = 0;
    if ( k == 0 ) {
        cout << n * n << endl;
        return 0;
    }
    for ( ll i = k + 1; i <= n; ++i ) {
        ll mod_group_num = ( n + 1 ) / i;
        ans += mod_group_num * ( i - k );
        ll num = ( n + 1 ) % i;
        ans += max(0LL, num - k);
    }
    cout << ans << endl;
    return 0;
}