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