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: Time Limit Exceeded)

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(void){
int a, b, c;
int n;
int count = 0;

scanf("%d", &n);

for(;;) {
srand(time(0));
a = rand () % n;
b = rand () % n;
c = rand () % n;
//printf("%d\n", a);
//printf("%d\n", b);
//printf("%d\n", c);   

if(n == a* b + c)
count++;
}

printf("%d", count);
    
}