import java.util.*;
public class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int c = 0;
        if (s.substring(0,1).equals("1")) c++;
        if (s.substring(1,2).equals("1")) c++;
        if (s.substring(2,3).equals("1")) c++;
        System.out.println(c);
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int c = 0;
        if (s.substring(0,1).equals("1")) c++;
        if (s.substring(1,2).equals("1")) c++;
        if (s.substring(2,3).equals("1")) c++;
        System.out.println(c);
	}
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int c = 0;
        if (s.substring(0,1).equals("1")) c++;
        if (s.substring(1,2).equals("1")) c++;
        if (s.substring(2,3).equals("1")) c++;
        System.out.println(c);
	} main {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int c = 0;
        if (s.substring(0,1).equals("1")) c++;
        if (s.substring(1,2).equals("1")) c++;
        if (s.substring(2,3).equals("1")) c++;
        System.out.println(c);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.next(); s sc.next() sc.next sc int c = 0; c 0 if (s.substring(0,1).equals("1")) c++; s.substring(0,1).equals("1") s.substring(0,1).equals s.substring(0,1) s.substring s 0 1 "1" c++ c if (s.substring(1,2).equals("1")) c++; s.substring(1,2).equals("1") s.substring(1,2).equals s.substring(1,2) s.substring s 1 2 "1" c++ c if (s.substring(2,3).equals("1")) c++; s.substring(2,3).equals("1") s.substring(2,3).equals s.substring(2,3) s.substring s 2 3 "1" c++ c System.out.println(c) System.out.println System.out System System.out c String[] args args public class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int c = 0;
        if (s.substring(0,1).equals("1")) c++;
        if (s.substring(1,2).equals("1")) c++;
        if (s.substring(2,3).equals("1")) c++;
        System.out.println(c);
	}
} public class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int c = 0;
        if (s.substring(0,1).equals("1")) c++;
        if (s.substring(1,2).equals("1")) c++;
        if (s.substring(2,3).equals("1")) c++;
        System.out.println(c);
	}
} Main
import java.util.*;
public class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int c = 0;
        if (s.substring(0,1).equals("1")) c++;
        if (s.substring(1,2).equals("1")) c++;
        if (s.substring(2,3).equals("1")) c++;
        System.out.println(c);
	}
}