public class Program
{
    public static void Main()
    {
        int num = int.Parse(Console.ReadLine() ?? string.Empty);
        //string[] str = (Console.ReadLine() ?? string.Empty).Trim().Split(' ');
        //string str = Console.ReadLine() ?? string.Empty;


        int a = num;
        //string str = num.ToString();
        while(a.ToString().Length > 1)
        { 
            int count = 0;
            for(int i = 0; i < a.ToString().Length;i++)
            {
                count +=int.Parse(a.ToString().Substring(i,1));
            }
            a = count;
        }
        Console.WriteLine(a);
    }
}