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>

int main(){

    long long N;

    long long cnt = 0;

    scanf("%lld", &N);

    long long num;

    for(long long i = 1; i <= N; i++){
        if(N%i == 0){
            num = (N/i) - 1;
            cnt += num;
        }else{
            num = N/i;
            cnt += num;
        }
    }

    printf("%lld\n", cnt);

    return 0;
}