import java.util.*;

public class Main {
    public static void main(String[] args){
        // Your code here!
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
    
        String[] strArr = str.split("");
        int count = 0;
        
        for(int i = 0; i <= (str.length() - 1); i++){
            if(strArr[i].equals("1")){
                count++;
            }   
        }
        System.out.println(count);

    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args){
        // Your code here!
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
    
        String[] strArr = str.split("");
        int count = 0;
        
        for(int i = 0; i <= (str.length() - 1); i++){
            if(strArr[i].equals("1")){
                count++;
            }   
        }
        System.out.println(count);

    }
} Main public static void main(String[] args){
        // Your code here!
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
    
        String[] strArr = str.split("");
        int count = 0;
        
        for(int i = 0; i <= (str.length() - 1); i++){
            if(strArr[i].equals("1")){
                count++;
            }   
        }
        System.out.println(count);

    } main {
        // Your code here!
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
    
        String[] strArr = str.split("");
        int count = 0;
        
        for(int i = 0; i <= (str.length() - 1); i++){
            if(strArr[i].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 String[] strArr = str.split(""); strArr str.split("") str.split str "" int count = 0; count 0 for(int i = 0; i <= (str.length() - 1); i++){
            if(strArr[i].equals("1")){
                count++;
            }   
        } int i = 0; int i = 0; i 0 i <= (str.length() - 1) i (str.length() - 1) str.length() str.length str 1 i++ i++ i {
            if(strArr[i].equals("1")){
                count++;
            }   
        } {
            if(strArr[i].equals("1")){
                count++;
            }   
        } if(strArr[i].equals("1")){
                count++;
            } strArr[i].equals("1") strArr[i].equals strArr[i] strArr 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){
        // Your code here!
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
    
        String[] strArr = str.split("");
        int count = 0;
        
        for(int i = 0; i <= (str.length() - 1); i++){
            if(strArr[i].equals("1")){
                count++;
            }   
        }
        System.out.println(count);

    }
} public class Main {
    public static void main(String[] args){
        // Your code here!
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
    
        String[] strArr = str.split("");
        int count = 0;
        
        for(int i = 0; i <= (str.length() - 1); i++){
            if(strArr[i].equals("1")){
                count++;
            }   
        }
        System.out.println(count);

    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args){
        // Your code here!
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
    
        String[] strArr = str.split("");
        int count = 0;
        
        for(int i = 0; i <= (str.length() - 1); i++){
            if(strArr[i].equals("1")){
                count++;
            }   
        }
        System.out.println(count);

    }
}
