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: Time Limit Exceeded)

#include<stdio.h>

int main() {
  int N = 0;
	int kumiawase = 0;
  
  
  scanf("%d", &N);
  
  for (int a = 1; a < N; a++) {
   for (int b = 1;  b < N; b++) {
    for (int c = 1; c < N; c++) {
      if ((a*b+c) == N) {
        kumiawase++;
      }
      }
  	}
  }
    
    printf("%d", kumiawase);
  
 	return 0; 
}