import java.util.*;
import java.util.stream.Stream;
 class Ideone
{
  public static void main(String[] args)
  {
   int number=55;

    
    Stream.iterate(String.valueOf(number),
               n -> String.valueOf(n.codePoints().map(Character::getNumericValue).sum()))
      .filter(s -> s.length()==1)
      .findFirst().ifPresent(System.out::println);
    
  }
}