using System.Collections.Generic;
using System;

public class Hello
{
    static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var p = int.Parse(line[0]) % 10;
        var q = int.Parse(line[1]) % 10;
        var r = int.Parse(line[2]) % 10;
        var k = long.Parse(line[3]);
        getAns(p, q, r, k);
    }
    static void getAns(int p, int q, int r, long k)
    {
        var d = new Dictionary<string, int>();
        for (int i = 4; i < 1010; i++)
        {
            var pqr = r.ToString() + q.ToString() + p.ToString();
            if (!d.ContainsKey(pqr)) d[pqr] = i;
            else
            {
                var loop = i - d[pqr];
                var fromloop = d[pqr];
                var targ = fromloop + (k - fromloop) % loop;
                foreach(var x in d)
                {
                    if (x.Value == targ)
                    {
                        var ans = 0;
                        foreach (var y in x.Key) ans += y - '0';
                        Console.WriteLine(ans % 10);
                        return;
                    }
                }
            }
            var a = (p + q + r) % 10;
            if (i == k) { Console.WriteLine(a); return; }
            p = q;
            q = r;
            r = a;
        }
    }
}