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 Fortran (GNU Fortran 9.2.1) (judge verdict: Accepted)

program c179

implicit none
integer :: n, a, z, c
real :: b

read *, n

z = 0

do a = 1, n
 b = real(n) / real(a)
 c = int(b)
 z = z + c
 if(a*c == n) then
  z = z - 1
 end if
end do

print *, z

end program c179