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>

int kake(int a){
  int i,count=0;
  for(i=1;i<=a;i++){
    if(a%i==0)
      count++;
  }
  return count;
}
int main(void){
  int i,A,B,C,N,kazu=0;
  scanf("%d",&N);
  for(C=1;C<N;C++)
    kazu+=kake(N-C);
  printf("%d\n",kazu);
  
  return 0;
}