import java.util.Scanner;

public class Main {

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

        int cnt = 0;
        for(int i =0; i < a.length(); i++){
            if(a.charAt(i)=='1'){
                cnt += 1;
            }
        }

        System.out.println(cnt);

    }
} import java.util.Scanner; Scanner java.util public class Main {

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

        int cnt = 0;
        for(int i =0; i < a.length(); i++){
            if(a.charAt(i)=='1'){
                cnt += 1;
            }
        }

        System.out.println(cnt);

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

        int cnt = 0;
        for(int i =0; i < a.length(); i++){
            if(a.charAt(i)=='1'){
                cnt += 1;
            }
        }

        System.out.println(cnt);

    } main {
        Scanner sc = new Scanner(System.in);
        String a = sc.next();

        int cnt = 0;
        for(int i =0; i < a.length(); i++){
            if(a.charAt(i)=='1'){
                cnt += 1;
            }
        }

        System.out.println(cnt);

    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String a = sc.next(); a sc.next() sc.next sc int cnt = 0; cnt 0 for(int i =0; i < a.length(); i++){
            if(a.charAt(i)=='1'){
                cnt += 1;
            }
        } int i =0; int i =0; i 0 i < a.length() i a.length() a.length a i++ i++ i {
            if(a.charAt(i)=='1'){
                cnt += 1;
            }
        } {
            if(a.charAt(i)=='1'){
                cnt += 1;
            }
        } if(a.charAt(i)=='1'){
                cnt += 1;
            } a.charAt(i)=='1' a.charAt(i) a.charAt a i '1' {
                cnt += 1;
            } cnt += 1 cnt 1 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 a = sc.next();

        int cnt = 0;
        for(int i =0; i < a.length(); i++){
            if(a.charAt(i)=='1'){
                cnt += 1;
            }
        }

        System.out.println(cnt);

    }
} public class Main {

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

        int cnt = 0;
        for(int i =0; i < a.length(); i++){
            if(a.charAt(i)=='1'){
                cnt += 1;
            }
        }

        System.out.println(cnt);

    }
} Main
import java.util.Scanner;

public class Main {

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

        int cnt = 0;
        for(int i =0; i < a.length(); i++){
            if(a.charAt(i)=='1'){
                cnt += 1;
            }
        }

        System.out.println(cnt);

    }
}
