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 a, b, c, n, flag = 0;
  scanf(" %d", &n);

  for(a = 1;a < n;a++)
  {
    for(b = 1;b < n;b++)
    {
      for(c = 1;c < n;c++)
      {
        if (a * b + c == n)
          flag++;
      }
    }
  }
  printf("%d\n", flag);
  return (0);
}