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
    n = num
    while n > 0 do
        sum += n % 10
        n = n.div(10)
    end
    sum
end
N = gets.to_i
min = 100
1.upto(N.div(2)) do |a|
    b = N - a
    min = [min, digit_sum(a) + digit_sum(b)].min
end
puts min