CDTS

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;


class Problem1
{
    static void Main()
    {

        string num = Console.ReadLine();
        int sum = 0;

        for (int i = 0; i < num.Length; i++)
        {
            if (num[i]-'0'<=9&&num[i]-'0'>=0)
            {
                sum += num[i] - '0';

            }
            else
            {
                continue;
            }
        }


        if (sum>9)
        {
            while (sum>9)
            {
                sum -= 9;


            }
        }
        Console.WriteLine(sum);






    }
}