import java.util.Scanner;

public class Main{
	public static void main(String[]args){
		Scanner sc=new Scanner(System.in);
		String a=sc.next();
		String s[]=new String[3];
		int count=0;
		s=a.split("");
		for(int i=0;i<3;i++){
			if(s[i].equals("1")){
				count++;
			}
		}

		System.out.println(count);

	}
} import java.util.Scanner; Scanner java.util public class Main{
	public static void main(String[]args){
		Scanner sc=new Scanner(System.in);
		String a=sc.next();
		String s[]=new String[3];
		int count=0;
		s=a.split("");
		for(int i=0;i<3;i++){
			if(s[i].equals("1")){
				count++;
			}
		}

		System.out.println(count);

	}
} Main public static void main(String[]args){
		Scanner sc=new Scanner(System.in);
		String a=sc.next();
		String s[]=new String[3];
		int count=0;
		s=a.split("");
		for(int i=0;i<3;i++){
			if(s[i].equals("1")){
				count++;
			}
		}

		System.out.println(count);

	} main {
		Scanner sc=new Scanner(System.in);
		String a=sc.next();
		String s[]=new String[3];
		int count=0;
		s=a.split("");
		for(int i=0;i<3;i++){
			if(s[i].equals("1")){
				count++;
			}
		}

		System.out.println(count);

	} Scanner sc=new Scanner(System.in); sc new Scanner(System.in) String a=sc.next(); a sc.next() sc.next sc String s[]=new String[3]; s new String[3] 3 int count=0; count 0 s=a.split("") s a.split("") a.split a "" for(int i=0;i<3;i++){
			if(s[i].equals("1")){
				count++;
			}
		} int i=0; int i=0; i 0 i<3 i 3 i++ i++ i {
			if(s[i].equals("1")){
				count++;
			}
		} {
			if(s[i].equals("1")){
				count++;
			}
		} if(s[i].equals("1")){
				count++;
			} s[i].equals("1") s[i].equals s[i] s 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){
		Scanner sc=new Scanner(System.in);
		String a=sc.next();
		String s[]=new String[3];
		int count=0;
		s=a.split("");
		for(int i=0;i<3;i++){
			if(s[i].equals("1")){
				count++;
			}
		}

		System.out.println(count);

	}
} public class Main{
	public static void main(String[]args){
		Scanner sc=new Scanner(System.in);
		String a=sc.next();
		String s[]=new String[3];
		int count=0;
		s=a.split("");
		for(int i=0;i<3;i++){
			if(s[i].equals("1")){
				count++;
			}
		}

		System.out.println(count);

	}
} Main
import java.util.Scanner;

public class Main{
	public static void main(String[]args){
		Scanner sc=new Scanner(System.in);
		String a=sc.next();
		String s[]=new String[3];
		int count=0;
		s=a.split("");
		for(int i=0;i<3;i++){
			if(s[i].equals("1")){
				count++;
			}
		}

		System.out.println(count);

	}
}
