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: Time Limit Exceeded)

#include <stdio.h>

int main(void)
{
    int i, j, k;
    int sum = 0;
    int result = 0;
    int n = 0;

    scanf("%d", &n);

    for(i = 1; i <= n; i++){
        for(j = 1; j < n; j++){
            for(k = 1; k < n; k++){
                sum = i * j + k;
                if(sum == n){
                    result++;
                }
            }
        }
    }
    printf("%d\n", result);

    return 0;


}