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 <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <math.h>

int main()
{
  int n,i,j;
  scanf("%d", &n);
  //printf("%d\n", n);
  double sqr = sqrt(n);
  int result = 0;
  for(i = 1;i < n; i++){
    for(j = 1;j < n; j++){
      if(i*j < n){
        result = result + 1;
      }else{
        break;
      }
    }
  }
  printf("%d\n", result);
  return 0;
}