import java.util.Scanner;

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

        String s = sc.nextLine();
        String[] str = new String[3];
        int count = 0;
        str = s.split("");
        for (int i = 0; i < str.length; i++)
            if (str[i].equals("1"))
                count++;
        System.out.println(count);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String s = sc.nextLine();
        String[] str = new String[3];
        int count = 0;
        str = s.split("");
        for (int i = 0; i < str.length; i++)
            if (str[i].equals("1"))
                count++;
        System.out.println(count);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String s = sc.nextLine();
        String[] str = new String[3];
        int count = 0;
        str = s.split("");
        for (int i = 0; i < str.length; i++)
            if (str[i].equals("1"))
                count++;
        System.out.println(count);
    } main {
        Scanner sc = new Scanner(System.in);

        String s = sc.nextLine();
        String[] str = new String[3];
        int count = 0;
        str = s.split("");
        for (int i = 0; i < str.length; i++)
            if (str[i].equals("1"))
                count++;
        System.out.println(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.nextLine(); s sc.nextLine() sc.nextLine sc String[] str = new String[3]; str new String[3] 3 int count = 0; count 0 str = s.split("") str s.split("") s.split s "" for (int i = 0; i < str.length; i++)
            if (str[i].equals("1"))
                count++; int i = 0; int i = 0; i 0 i < str.length i str.length str str.length i++ i++ i if (str[i].equals("1"))
                count++; if (str[i].equals("1"))
                count++; str[i].equals("1") str[i].equals str[i] str 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) {
        Scanner sc = new Scanner(System.in);

        String s = sc.nextLine();
        String[] str = new String[3];
        int count = 0;
        str = s.split("");
        for (int i = 0; i < str.length; i++)
            if (str[i].equals("1"))
                count++;
        System.out.println(count);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String s = sc.nextLine();
        String[] str = new String[3];
        int count = 0;
        str = s.split("");
        for (int i = 0; i < str.length; i++)
            if (str[i].equals("1"))
                count++;
        System.out.println(count);
    }
} Main
import java.util.Scanner;

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

        String s = sc.nextLine();
        String[] str = new String[3];
        int count = 0;
        str = s.split("");
        for (int i = 0; i < str.length; i++)
            if (str[i].equals("1"))
                count++;
        System.out.println(count);
    }
}