import java.util.Scanner;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String[] S = sc.next().split("");
    int ans = 0;
      
      for(String s : S){
        if(s.equals("1")){
        	ans++;
        }
      }
    System.out.println(ans);
  }
} import java.util.Scanner; Scanner java.util public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String[] S = sc.next().split("");
    int ans = 0;
      
      for(String s : S){
        if(s.equals("1")){
        	ans++;
        }
      }
    System.out.println(ans);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String[] S = sc.next().split("");
    int ans = 0;
      
      for(String s : S){
        if(s.equals("1")){
        	ans++;
        }
      }
    System.out.println(ans);
  } main {
    Scanner sc = new Scanner(System.in);
    String[] S = sc.next().split("");
    int ans = 0;
      
      for(String s : S){
        if(s.equals("1")){
        	ans++;
        }
      }
    System.out.println(ans);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String[] S = sc.next().split(""); S sc.next().split("") sc.next().split sc.next() sc.next sc "" int ans = 0; ans 0 for(String s : S){
        if(s.equals("1")){
        	ans++;
        }
      } String s S {
        if(s.equals("1")){
        	ans++;
        }
      } {
        if(s.equals("1")){
        	ans++;
        }
      } if(s.equals("1")){
        	ans++;
        } s.equals("1") s.equals s "1" {
        	ans++;
        } ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String[] S = sc.next().split("");
    int ans = 0;
      
      for(String s : S){
        if(s.equals("1")){
        	ans++;
        }
      }
    System.out.println(ans);
  }
} public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String[] S = sc.next().split("");
    int ans = 0;
      
      for(String s : S){
        if(s.equals("1")){
        	ans++;
        }
      }
    System.out.println(ans);
  }
} Main
import java.util.Scanner;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String[] S = sc.next().split("");
    int ans = 0;
      
      for(String s : S){
        if(s.equals("1")){
        	ans++;
        }
      }
    System.out.println(ans);
  }
}