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(num)
  sum = 0
  while num > 0 do
    sum += num % 10
    num /= 10
  end
  sum
end

n = gets.to_i

min = n
1.upto(n / 2) do |i|
  digit_sum = digit_sum(i) + digit_sum(n - i)
  min = digit_sum if min > digit_sum
end

puts min