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: Accepted)

#include <stdio.h>

int main() {
    int N, count, a, b, f, i;

    scanf("%d", & N);

    count = 0;
    for (a = 1; a <= N; a++) {
        f = 0;
        for (b = 1; b <= N; b++) {
            i = a * b;
            if (i >= N) {
                break;
            }
            count++;
            f = 1;
        }
        if (!f) {
            break;
        }
    }

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