Problem:
Score : 200 points

Problem Statement

Takahashi has two positive integers A and B.

It is known that A plus B equals N.
Find the minimum possible value of "the sum of the digits of A" plus "the sum of the digits of B" (in base 10).

Constraints

2 ≤ N ≤ 10^5

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the minimum possible value of "the sum of the digits of A" plus "the sum of the digits of B".

Sample Input 1

15

Sample Output 1

6

When A=2 and B=13, the sums of their digits are 2 and 4, which minimizes the value in question.

Sample Input 2

100000

Sample Output 2

10

Solution in Ruby (2.3.3) (judge verdict: Accepted)

require 'set'; require 'prime'
INF=Float::INFINITY; MOD=10**9+7
n = gets.chomp.to_i

def dsum(n)
  n.to_s.split(//).map(&:to_i).inject(&:+)
end

ans = INF
1.upto(n/2+1).each do |x|
  y = n - x
  sum = dsum(y) + dsum(x)
  ans = sum if ans > sum
end

puts ans