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 <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <map>
#include <set>
#include <vector>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <numeric>
#include <functional>
using namespace std;

#define Rep(b, e, i) for(int i = b; i <= e; i++)
#define rep(n, i) Rep(0, n-1, i)

const int MAX = 200000;
const double PI = 3.14159265358979323846;
const double EPS = 1e-12;
const int INF = 1<<31-1;
const int MOD = 1000000007;

int dx4[4]={1,0,-1,0};
int dy4[4]={0,1,0,-1};
int dx8[8]={1,0,-1,1,-1,1,0,-1};
int dy8[8]={1,1,1,0,0,-1,-1,-1};

typedef long long ll;
typedef pair<ll, ll> llP;
typedef pair<int, int> intP;
typedef std::priority_queue<int> IntPrioQueue; //Z->A
typedef std::priority_queue<int, std::vector<int>, std::greater<int> > IntReversePrioQueue; //A->Z

void solve(void){
    int N, K;
    cin >> N >> K;
    ll ans = 0;
    Rep(1, N, b){
        //cout << ans << '\n';
        ans += max(0, b-K)*(N/b)+max(0,N%b-K+1)-(K==0?1:0);
    }
    cout << ans << '\n';
}

int main(void){
  solve();
  return 0;
}