import java.util.*;
public class Main {
	public static void main(String[] args) throws Exception {
		 
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        sc.close();
        
        int count = 0;
        
        for(int i = 0; i < str.length(); i++){
            String tempStr = String.valueOf(str.charAt(i));
            
            if(tempStr.equals("1")){
                count++;
            } 
        }
        
        System.out.println(count);
    }
} import java.util.*; util.* java public class Main {
	public static void main(String[] args) throws Exception {
		 
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        sc.close();
        
        int count = 0;
        
        for(int i = 0; i < str.length(); i++){
            String tempStr = String.valueOf(str.charAt(i));
            
            if(tempStr.equals("1")){
                count++;
            } 
        }
        
        System.out.println(count);
    }
} Main public static void main(String[] args) throws Exception {
		 
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        sc.close();
        
        int count = 0;
        
        for(int i = 0; i < str.length(); i++){
            String tempStr = String.valueOf(str.charAt(i));
            
            if(tempStr.equals("1")){
                count++;
            } 
        }
        
        System.out.println(count);
    } main {
		 
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        sc.close();
        
        int count = 0;
        
        for(int i = 0; i < str.length(); i++){
            String tempStr = String.valueOf(str.charAt(i));
            
            if(tempStr.equals("1")){
                count++;
            } 
        }
        
        System.out.println(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String str = sc.next(); str sc.next() sc.next sc sc.close() sc.close sc int count = 0; count 0 for(int i = 0; i < str.length(); i++){
            String tempStr = String.valueOf(str.charAt(i));
            
            if(tempStr.equals("1")){
                count++;
            } 
        } int i = 0; int i = 0; i 0 i < str.length() i str.length() str.length str i++ i++ i {
            String tempStr = String.valueOf(str.charAt(i));
            
            if(tempStr.equals("1")){
                count++;
            } 
        } {
            String tempStr = String.valueOf(str.charAt(i));
            
            if(tempStr.equals("1")){
                count++;
            } 
        } String tempStr = String.valueOf(str.charAt(i)); tempStr String.valueOf(str.charAt(i)) String.valueOf String str.charAt(i) str.charAt str i if(tempStr.equals("1")){
                count++;
            } tempStr.equals("1") tempStr.equals tempStr "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) throws Exception {
		 
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        sc.close();
        
        int count = 0;
        
        for(int i = 0; i < str.length(); i++){
            String tempStr = String.valueOf(str.charAt(i));
            
            if(tempStr.equals("1")){
                count++;
            } 
        }
        
        System.out.println(count);
    }
} public class Main {
	public static void main(String[] args) throws Exception {
		 
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        sc.close();
        
        int count = 0;
        
        for(int i = 0; i < str.length(); i++){
            String tempStr = String.valueOf(str.charAt(i));
            
            if(tempStr.equals("1")){
                count++;
            } 
        }
        
        System.out.println(count);
    }
} Main
import java.util.*;
public class Main {
	public static void main(String[] args) throws Exception {
		 
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        sc.close();
        
        int count = 0;
        
        for(int i = 0; i < str.length(); i++){
            String tempStr = String.valueOf(str.charAt(i));
            
            if(tempStr.equals("1")){
                count++;
            } 
        }
        
        System.out.println(count);
    }
}