import java.util.*;
public class Main {
    public static void main(String[] args) {
        // System.out.println(new App().getGreeting());
        Scanner sc = new Scanner(System.in);

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

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

        String s = sc.next();
        int cnt = 0;
        for(int i = 0; i < s.length(); i++){
            cnt += (s.charAt(i)== '1' ? 1 : 0);
        }
        System.out.println(cnt);
    } main {
        // System.out.println(new App().getGreeting());
        Scanner sc = new Scanner(System.in);

        String s = sc.next();
        int cnt = 0;
        for(int i = 0; i < s.length(); i++){
            cnt += (s.charAt(i)== '1' ? 1 : 0);
        }
        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 for(int i = 0; i < s.length(); i++){
            cnt += (s.charAt(i)== '1' ? 1 : 0);
        } int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
            cnt += (s.charAt(i)== '1' ? 1 : 0);
        } {
            cnt += (s.charAt(i)== '1' ? 1 : 0);
        } cnt += (s.charAt(i)== '1' ? 1 : 0) cnt (s.charAt(i)== '1' ? 1 : 0) s.charAt(i)== '1' s.charAt(i) s.charAt s i '1' 1 0 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) {
        // System.out.println(new App().getGreeting());
        Scanner sc = new Scanner(System.in);

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

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

        String s = sc.next();
        int cnt = 0;
        for(int i = 0; i < s.length(); i++){
            cnt += (s.charAt(i)== '1' ? 1 : 0);
        }
        System.out.println(cnt);
    }
}
