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 main(){

    // 変数の宣言・読み込み
    int n,ans=0;
  	long a,b;
    scanf("%d", &n);

    for(a=1;a<n;a++){
      for(b=a;a*b<n;b++){
        if(a==b){
          ans++;
        }else{
          ans=ans+2;
          }
      }
    }

    printf("%d", ans);
    return 0;
}