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;
long long read() { 
    bool flag = true; long long num = 0;char c = getchar(); 
    for(;c < '0' || c > '9';c = getchar())if(c == '-') flag = false; 
    for(;c >= '0' && c <= '9';c = getchar()) num = ( num << 3 ) + ( num << 1 ) + c - 48; 
    if(flag) return num;  else return -num; 
}
int main(){
	long long n,k;
	n = read();
	k=read();
	long long ans=0;
	if(k==0) {
		printf("%d",n);
		exit(0);
	}
	for(int i=k+1;i<=n;++i) { 
     long long a,b;
	 a=n/i;
	 b=n%i;
	 ans=ans+a*(i-k);
	 if(a*i+k<=n)
	  ans=ans+n-(a*i+k)+1;
	} 
	cout<<ans;
	return 0;
}