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 Pascal (FPC 3.0.4) (judge verdict: Accepted)

program test;
{$mode objfpc}{$H+}{$R+}{$S+}
Uses sysutils,math;
var
	N	        :integer;
	a,b,ans     :integer;
begin
    readln(N);
    ans:=0;
    for a:=1 to N do
    begin
        for b:=1 to (N div a) do
        begin
            if ((a*b)<N) then inc(ans);
        end;
    end;

    writeln(stdout,ans);
end.