class RecursiveDigitSum
{
    // https://www.hackerrank.com/challenges/recursive-digit-sum/problem 

    public RecursiveDigitSum()
    {
        string[] tokens = Console.ReadLine().Split(' ');
        string n = tokens[0];
        int k = Convert.ToInt32(tokens[1]);

        string str = string.Concat(Enumerable.Repeat(n, k));
        int result = Solve(str);
        Console.WriteLine(result);
        Console.ReadLine();
    }

    private int Solve(string str)
    {
        int count = 0;

        foreach (char c in str)
        {
            count += (int)Char.GetNumericValue(c);
        }

        string sRet = count.ToString();

        if (count % 10 == count)
            return count;
        else
            return Solve(sRet);
    }
}