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>
#define _USE_MATH_DEFINES
#include <math.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <string.h>


int N_all;


int main(int argc, char* argv[]){
    int i,j,sqrti;
    int count,now;
    double i_d;
    count=0;
    scanf("%d",&N_all);
    for(i=1;i<=N_all-1;i++){
        i_d = 1.*i;
        sqrti = sqrt(i_d);
        if((sqrti+1)*(sqrti+1) == i){
            sqrti ++;
        }
        for(j=1;j<=sqrti;j++){
            //printf("%d %d %d %d\n",i,j,N_all-i,(i/j)*j+(N_all-i) );
            if(i%j == 0){
                //printf("count\n");
                count++;
                if(j!=sqrti || sqrti*sqrti!=i){
                    count++;
                }
            }
        }
    }
    printf("%d",count);
    return 0;
}