import java.util.*;
public class Test11 {
  public static void main(String[] args){
    Scanner sc=new Scanner(System.in);
    String[] line;
    line=sc.nextLine().split(" ");
    int n=Integer.parseInt(line[0]);
    for(int i=1;i<100;i++){
      int tmp=n;
      n=0;
      while(tmp>0){
        n+=tmp%10;
        tmp=tmp/10;
      }
    }
    String result=""+n;
    System.out.println(result);
  }
}