using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static long[] NList => ReadLine().Split().Select(long.Parse).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        for (var i = 0; i < 99; ++i)
        {
            var tmp = n;
            var sum = 0;
            while (tmp > 0)
            {
                sum += tmp % 10;
                tmp /= 10;
            }
            n = sum;
        }
        WriteLine(n);
    }
}