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: Wrong Answer)

#include <stdio.h>
int main(void){
	int n,a,b,c,i,j,f=0,ans;
	scanf("%d",&n);
	for(c=1;c<n;c++){
		ans=n-c;
		for(a=1;a<=(ans/2);a++){
			if(ans%a==0){
				
				if(ans/a==a){
					f++;
				}else{
					f+=2;
				}
				//printf("%d %d\n",a,c);
				
			}
		}
	}
	printf("%d\n",f);
	return 0;
}