import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		
	Scanner scan = new Scanner(System.in);
	String str = scan.next();
	
	String[] strArray = str.split("");
	
	int count = 0;
	
	for(int i = 0; i < strArray.length ; i++ ) {
	if(strArray[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 scan = new Scanner(System.in);
	String str = scan.next();
	
	String[] strArray = str.split("");
	
	int count = 0;
	
	for(int i = 0; i < strArray.length ; i++ ) {
	if(strArray[i].equals("1")) {
		count++;
	  }
	 }
	System.out.println(count);
	}
} Main public static void main(String[] args){
		
	Scanner scan = new Scanner(System.in);
	String str = scan.next();
	
	String[] strArray = str.split("");
	
	int count = 0;
	
	for(int i = 0; i < strArray.length ; i++ ) {
	if(strArray[i].equals("1")) {
		count++;
	  }
	 }
	System.out.println(count);
	} main {
		
	Scanner scan = new Scanner(System.in);
	String str = scan.next();
	
	String[] strArray = str.split("");
	
	int count = 0;
	
	for(int i = 0; i < strArray.length ; i++ ) {
	if(strArray[i].equals("1")) {
		count++;
	  }
	 }
	System.out.println(count);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) String str = scan.next(); str scan.next() scan.next scan String[] strArray = str.split(""); strArray str.split("") str.split str "" int count = 0; count 0 for(int i = 0; i < strArray.length ; i++ ) {
	if(strArray[i].equals("1")) {
		count++;
	  }
	 } int i = 0; int i = 0; i 0 i < strArray.length i strArray.length strArray strArray.length i++ i++ i {
	if(strArray[i].equals("1")) {
		count++;
	  }
	 } {
	if(strArray[i].equals("1")) {
		count++;
	  }
	 } if(strArray[i].equals("1")) {
		count++;
	  } strArray[i].equals("1") strArray[i].equals strArray[i] strArray 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 scan = new Scanner(System.in);
	String str = scan.next();
	
	String[] strArray = str.split("");
	
	int count = 0;
	
	for(int i = 0; i < strArray.length ; i++ ) {
	if(strArray[i].equals("1")) {
		count++;
	  }
	 }
	System.out.println(count);
	}
} public class Main {
	public static void main(String[] args){
		
	Scanner scan = new Scanner(System.in);
	String str = scan.next();
	
	String[] strArray = str.split("");
	
	int count = 0;
	
	for(int i = 0; i < strArray.length ; i++ ) {
	if(strArray[i].equals("1")) {
		count++;
	  }
	 }
	System.out.println(count);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		
	Scanner scan = new Scanner(System.in);
	String str = scan.next();
	
	String[] strArray = str.split("");
	
	int count = 0;
	
	for(int i = 0; i < strArray.length ; i++ ) {
	if(strArray[i].equals("1")) {
		count++;
	  }
	 }
	System.out.println(count);
	}
}