import java.util.*;
public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        List<String> numbers = Arrays.asList(sc.nextLine().split(""));
        
        int count = 0;
        for (String number : numbers) {
            if (number.equals("1")) {
                count++;
            }
        }
        System.out.println(count);
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        List<String> numbers = Arrays.asList(sc.nextLine().split(""));
        
        int count = 0;
        for (String number : numbers) {
            if (number.equals("1")) {
                count++;
            }
        }
        System.out.println(count);
	}
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        List<String> numbers = Arrays.asList(sc.nextLine().split(""));
        
        int count = 0;
        for (String number : numbers) {
            if (number.equals("1")) {
                count++;
            }
        }
        System.out.println(count);
	} main {
        Scanner sc = new Scanner(System.in);
        List<String> numbers = Arrays.asList(sc.nextLine().split(""));
        
        int count = 0;
        for (String number : numbers) {
            if (number.equals("1")) {
                count++;
            }
        }
        System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) List<String> numbers = Arrays.asList(sc.nextLine().split("")); numbers Arrays.asList(sc.nextLine().split("")) Arrays.asList Arrays sc.nextLine().split("") sc.nextLine().split sc.nextLine() sc.nextLine sc "" int count = 0; count 0 for (String number : numbers) {
            if (number.equals("1")) {
                count++;
            }
        } String number numbers {
            if (number.equals("1")) {
                count++;
            }
        } {
            if (number.equals("1")) {
                count++;
            }
        } if (number.equals("1")) {
                count++;
            } number.equals("1") number.equals number "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){
        Scanner sc = new Scanner(System.in);
        List<String> numbers = Arrays.asList(sc.nextLine().split(""));
        
        int count = 0;
        for (String number : numbers) {
            if (number.equals("1")) {
                count++;
            }
        }
        System.out.println(count);
	}
} public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        List<String> numbers = Arrays.asList(sc.nextLine().split(""));
        
        int count = 0;
        for (String number : numbers) {
            if (number.equals("1")) {
                count++;
            }
        }
        System.out.println(count);
	}
} Main
import java.util.*;
public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        List<String> numbers = Arrays.asList(sc.nextLine().split(""));
        
        int count = 0;
        for (String number : numbers) {
            if (number.equals("1")) {
                count++;
            }
        }
        System.out.println(count);
	}
}