Competitions

# БГУ Личное Первенство

# Stepan and pairs

Recently Stepan is very interested in pairs of numbers, and instead of pairs he is interested in greater common divisor, lets denote it as GCD(x, y). Now Stepan has an integer n and he is interested in the next information: how many pairs of integers (i, j) exist such that 1 ≤ i, j ≤ n and i = GCD(i, j).

Help him to solve this problem.

## Input data

One integer n (1 ≤ n ≤ `10^6`

).

## Output data

Print the number of required pairs.

## Examples

Input example #1

1

Output example #1

1

Input example #2

4

Output example #2

8

Input example #3

10

Output example #3

27