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: Wrong Answer)

n = gets.to_i
min = 9

(0..n).each do |a|
  (0..n).each do |b|
    sum = a + b

    next if n != sum
    a1 = a
    b1 = b
    sum_a = 0
    sum_b = 0
    until a1 == 0
      sum_a += a1 % 10
      a1 /= 10
    end

    until b1 == 0
      sum_b += b1%10
      b1 /= 10
    end
    total = sum_a + sum_b
    min = total if min > total && n == sum
  end
end

puts min