import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);

        String s = sc.next();
        int cnt = 0;
        int n = s.length();

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

        String s = sc.next();
        int cnt = 0;
        int n = s.length();

        for(int i = 0; i < n; i++){
            if(s.charAt(i) == '1'){
                cnt++;
            }
        }
        System.out.println(cnt);
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);

        String s = sc.next();
        int cnt = 0;
        int n = s.length();

        for(int i = 0; i < n; i++){
            if(s.charAt(i) == '1'){
                cnt++;
            }
        }
        System.out.println(cnt);
    } main {
        Scanner sc = new Scanner(System.in);

        String s = sc.next();
        int cnt = 0;
        int n = s.length();

        for(int i = 0; i < n; i++){
            if(s.charAt(i) == '1'){
                cnt++;
            }
        }
        System.out.println(cnt);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.next(); s sc.next() sc.next sc int cnt = 0; cnt 0 int n = s.length(); n s.length() s.length s for(int i = 0; i < n; i++){
            if(s.charAt(i) == '1'){
                cnt++;
            }
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            if(s.charAt(i) == '1'){
                cnt++;
            }
        } {
            if(s.charAt(i) == '1'){
                cnt++;
            }
        } if(s.charAt(i) == '1'){
                cnt++;
            } s.charAt(i) == '1' s.charAt(i) s.charAt s i '1' {
                cnt++;
            } cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);

        String s = sc.next();
        int cnt = 0;
        int n = s.length();

        for(int i = 0; i < n; i++){
            if(s.charAt(i) == '1'){
                cnt++;
            }
        }
        System.out.println(cnt);
    }
} public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);

        String s = sc.next();
        int cnt = 0;
        int n = s.length();

        for(int i = 0; i < n; i++){
            if(s.charAt(i) == '1'){
                cnt++;
            }
        }
        System.out.println(cnt);
    }
} Main
import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);

        String s = sc.next();
        int cnt = 0;
        int n = s.length();

        for(int i = 0; i < n; i++){
            if(s.charAt(i) == '1'){
                cnt++;
            }
        }
        System.out.println(cnt);
    }
}