import java.util.*;

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

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