import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {

        Scanner sc = new Scanner(System.in);
        
        String N = sc.next();
        int count = 0;
        
        for(int i = 0; i < 3; i++){
            if( N.charAt(i) == '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 N = sc.next();
        int count = 0;
        
        for(int i = 0; i < 3; i++){
            if( N.charAt(i) == '1') count++;
        }
        System.out.println(count);
    }
} Main public static void main(String[] args) throws Exception {

        Scanner sc = new Scanner(System.in);
        
        String N = sc.next();
        int count = 0;
        
        for(int i = 0; i < 3; i++){
            if( N.charAt(i) == '1') count++;
        }
        System.out.println(count);
    } main {

        Scanner sc = new Scanner(System.in);
        
        String N = sc.next();
        int count = 0;
        
        for(int i = 0; i < 3; i++){
            if( N.charAt(i) == '1') count++;
        }
        System.out.println(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String N = sc.next(); N sc.next() sc.next sc int count = 0; count 0 for(int i = 0; i < 3; i++){
            if( N.charAt(i) == '1') count++;
        } int i = 0; int i = 0; i 0 i < 3 i 3 i++ i++ i {
            if( N.charAt(i) == '1') count++;
        } {
            if( N.charAt(i) == '1') count++;
        } if( N.charAt(i) == '1') count++; N.charAt(i) == '1' N.charAt(i) N.charAt N i '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) throws Exception {

        Scanner sc = new Scanner(System.in);
        
        String N = sc.next();
        int count = 0;
        
        for(int i = 0; i < 3; i++){
            if( N.charAt(i) == '1') count++;
        }
        System.out.println(count);
    }
} public class Main {
    public static void main(String[] args) throws Exception {

        Scanner sc = new Scanner(System.in);
        
        String N = sc.next();
        int count = 0;
        
        for(int i = 0; i < 3; i++){
            if( N.charAt(i) == '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 N = sc.next();
        int count = 0;
        
        for(int i = 0; i < 3; i++){
            if( N.charAt(i) == '1') count++;
        }
        System.out.println(count);
    }
}
