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 Python (3.8.2) (judge verdict: Accepted)

N = int(input())
NR = int(N**0.5)
count = 0
if int(N/2)-N/2 == 0:
    for i in range(1,int(N/2)):
        if int(N/i)-N/i == 0:
            count += int(N/i)-1
        else:
            count += int(N/i)
else:
    for i in range(1,int(N/2)+1):
        if int(N/i)-N/i == 0:
            count += int(N/i)-1
        else:
            count += int(N/i)

count += int(N/2)
print(count)