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 (Clang 10.0.0) (judge verdict: Accepted)

#include<stdio.h>

int main(void){
	int N;
	int ans=0;
	
	scanf("%d",&N);
    
	for(int i=1;i<N;i++){
		if(N%i==0){
			ans+=N/i-1;
		}
		else{
			ans+=N/i;
		}
	}

	printf("%d\n",ans);

	return 0;
}