import java.util.*;

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

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