Problem:
Score : 300 points

Problem Statement

Given is a positive integer N.
How many tuples (A,B,C) of positive integers satisfy A \times B + C = N?

Constraints

2 \leq N \leq 10^6

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer.

Sample Input 1

3

Sample Output 1

3

There are 3 tuples of integers that satisfy A \times B + C = 3: (A, B, C) = (1, 1, 2), (1, 2, 1), (2, 1, 1).

Sample Input 2

100

Sample Output 2

473

Sample Input 3

1000000

Sample Output 3

13969985

Solution in C (GCC 9.2.1) (judge verdict: Accepted)

#include<stdio.h>
#include<math.h>
int mene(int num){
	int toori=0;
	for(int i=1;i<=sqrt(num);i++){
		if((num/i)*i==num){
			toori+=2;
		}
		if(num==i*i)toori--;
	}
	return(toori);
}
int main()
{
   int ans=0;
   int n;
   scanf("%d",&n);
    for(int i=1;i<n;i++){
		ans+=mene(i);
   }
   printf("%d",ans);
}