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# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;

namespace AtCoder
{
	public class Program
	{
		static void Main()
		{
			int n = int.Parse(Console.ReadLine());

			int DigitSum(int v)
			{
				int sum = 0;
				while (v > 0) {
					sum += v % 10;
					v /= 10;
				}

				return sum;
			}

			int ans = int.MaxValue;
			for (int i = 1; i < n; i++) {
				int a = i;
				int b = n - i;

				int sum = DigitSum(a) + DigitSum(b);
				ans = Math.Min(ans, sum);
			}

			Console.WriteLine(ans);
		}
	}
}