import java.util.*;

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

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