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>
int div(int n)
{
  int i;
  int ans=0;
  for (i=1;i*i<=n;i++){
    if (n%i==0){
	    ans+=1;
    if (i != n/i)
      ans+=1;
    }
  }
  return ans;
}
int main(){
  int s,a,j;
  scanf("%d\n",&s);
  a=1;
  for (j=2;j<s;j++){
    a+=div(j);
  }
  printf("%d",a);
}