import java.util.*;
public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        int count = 0;
        
        if(s.charAt(0) == '1')count++;
        if(s.charAt(1) == '1')count++;
        if(s.charAt(2) == '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 s = sc.nextLine();
        int count = 0;
        
        if(s.charAt(0) == '1')count++;
        if(s.charAt(1) == '1')count++;
        if(s.charAt(2) == '1')count++;
		
        System.out.println(count);
	 }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        int count = 0;
        
        if(s.charAt(0) == '1')count++;
        if(s.charAt(1) == '1')count++;
        if(s.charAt(2) == '1')count++;
		
        System.out.println(count);
	 } main {
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        int count = 0;
        
        if(s.charAt(0) == '1')count++;
        if(s.charAt(1) == '1')count++;
        if(s.charAt(2) == '1')count++;
		
        System.out.println(count);
	 } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.nextLine(); s sc.nextLine() sc.nextLine sc int count = 0; count 0 if(s.charAt(0) == '1')count++; s.charAt(0) == '1' s.charAt(0) s.charAt s 0 '1' count++ count if(s.charAt(1) == '1')count++; s.charAt(1) == '1' s.charAt(1) s.charAt s 1 '1' count++ count if(s.charAt(2) == '1')count++; s.charAt(2) == '1' s.charAt(2) s.charAt s 2 '1' 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 s = sc.nextLine();
        int count = 0;
        
        if(s.charAt(0) == '1')count++;
        if(s.charAt(1) == '1')count++;
        if(s.charAt(2) == '1')count++;
		
        System.out.println(count);
	 }
} public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        int count = 0;
        
        if(s.charAt(0) == '1')count++;
        if(s.charAt(1) == '1')count++;
        if(s.charAt(2) == '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 s = sc.nextLine();
        int count = 0;
        
        if(s.charAt(0) == '1')count++;
        if(s.charAt(1) == '1')count++;
        if(s.charAt(2) == '1')count++;
		
        System.out.println(count);
	 }
}
