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

namespace test_math
{
    class Program
    {
        static void Main(string[] args)
        {
            int number = int.Parse(Console.ReadLine());
            int a = number / 1000;
            int b = number / 100 % 10;
            int c = number / 10 % 10;
            int d = number % 10;

            int result = a + b + c + d;
            Console.WriteLine(result);
        }
    }
}