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>
#include <math.h>

int main(){
    int N;
    scanf("%d", &N);
    double p = pow(N-1, N);

    int A=1, B=1, C=1, cnt=0;
    for(int i=0; i<p; i++){
        if(A*B+C==N){
            cnt++;
        }
        C++;
        if(C==N){
            B++;
            C=1;
            if(B==N){
                A++;
                B=1;
            }
        }
    }

    printf("%d\n", cnt);
    return 0;
}