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