import java.util.*;
import java.io.*;
import java.lang.*;

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

        int ans = 0;

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

        System.out.println(ans);
    }
} import java.util.*; util.* java import java.io.*; io.* java import java.lang.*; lang.* java public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String a = sc.next();

        int ans = 0;

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

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

        int ans = 0;

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

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

        int ans = 0;

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

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

        int ans = 0;

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

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

        int ans = 0;

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

        System.out.println(ans);
    }
} Main
import java.util.*;
import java.io.*;
import java.lang.*;

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

        int ans = 0;

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

        System.out.println(ans);
    }
}
