using System;

class Program
{
    static void Main(string[] args)
    {
        var N = int.Parse(Console.ReadLine());
        var ans = N;
        for (int i = 2; i <= 100; i++)
        {
            var sum = 0;
            while (ans != 0)
            {
                sum += ans % 10;
                ans /= 10;
            }
            ans = sum;
            if (sum / 10 == 0) break;
        }
        Console.WriteLine(ans);
    }
}