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)

def digit_sum(x)
  x.to_s.split('').map{|c| c.ord - '0'.ord}.reduce('+')
end

def calc(a, b)
  digit_sum(a) + digit_sum(b)
end

def main(argv)
  n = gets.chomp.to_i

  m =1e+9.to_i
  (1..((n + 1) / 2)).each do |a|
    b = n - a
    m = [m, calc(a, b)].min
  end
  puts m.to_s
end

if self.to_s == 'main' then
  main(ARGV)
end