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 (Clang 10.0.0) (judge verdict: Accepted)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
//KMP算法练习
long long ans=0;


int main(){
    int i;
    int  n;
    scanf("%d",&n);
    for(i=1;i<n;i++){
        if(n%i==0){
            ans=ans+(n/i)-1;
            
        }
        else{
            ans+=(n/i);
            
        }
    }
    
    
    printf("%d",ans);
}