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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System.Linq.Expressions;
using System;
namespace ExpressionQiita
{
    class Program
    {
        static void Main(string[] args)
        {
            int min = 0;
            int N = int.Parse(Console.ReadLine());
            for (int A = 1;A < N;A++)
            {
                int B = N - A;
                int sum = isum(A) + isum(B);
                min = (min > sum || min == 0)?sum:min;
            }
            Console.WriteLine(min);
        }

        public static int isum(int num)
        {
            int sum = 0;
            do
            {
                int dig = num % 10;
                sum += dig;
                num = num / 10;
            } while (num != 0);
            return sum;
        }
    }
}