import java.util.*;

public class Main{
  
  public static void main (String[] args){
  
  	Scanner scanner = new Scanner (System.in);
  
 	String number = scanner.nextLine();
    
  	int count = 0;
    
  	for (int i=0; i<3; i++){
  		char temp = number.charAt(i);
  		
      	if (temp == '1'){
          count++;
        }
    }
    System.out.println(count);
  }
} import java.util.*; util.* java public class Main{
  
  public static void main (String[] args){
  
  	Scanner scanner = new Scanner (System.in);
  
 	String number = scanner.nextLine();
    
  	int count = 0;
    
  	for (int i=0; i<3; i++){
  		char temp = number.charAt(i);
  		
      	if (temp == '1'){
          count++;
        }
    }
    System.out.println(count);
  }
} Main public static void main (String[] args){
  
  	Scanner scanner = new Scanner (System.in);
  
 	String number = scanner.nextLine();
    
  	int count = 0;
    
  	for (int i=0; i<3; i++){
  		char temp = number.charAt(i);
  		
      	if (temp == '1'){
          count++;
        }
    }
    System.out.println(count);
  } main {
  
  	Scanner scanner = new Scanner (System.in);
  
 	String number = scanner.nextLine();
    
  	int count = 0;
    
  	for (int i=0; i<3; i++){
  		char temp = number.charAt(i);
  		
      	if (temp == '1'){
          count++;
        }
    }
    System.out.println(count);
  } Scanner scanner = new Scanner (System.in); scanner new Scanner (System.in) String number = scanner.nextLine(); number scanner.nextLine() scanner.nextLine scanner int count = 0; count 0 for (int i=0; i<3; i++){
  		char temp = number.charAt(i);
  		
      	if (temp == '1'){
          count++;
        }
    } int i=0; int i=0; i 0 i<3 i 3 i++ i++ i {
  		char temp = number.charAt(i);
  		
      	if (temp == '1'){
          count++;
        }
    } {
  		char temp = number.charAt(i);
  		
      	if (temp == '1'){
          count++;
        }
    } char temp = number.charAt(i); temp number.charAt(i) number.charAt number i if (temp == '1'){
          count++;
        } temp == '1' temp '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 scanner = new Scanner (System.in);
  
 	String number = scanner.nextLine();
    
  	int count = 0;
    
  	for (int i=0; i<3; i++){
  		char temp = number.charAt(i);
  		
      	if (temp == '1'){
          count++;
        }
    }
    System.out.println(count);
  }
} public class Main{
  
  public static void main (String[] args){
  
  	Scanner scanner = new Scanner (System.in);
  
 	String number = scanner.nextLine();
    
  	int count = 0;
    
  	for (int i=0; i<3; i++){
  		char temp = number.charAt(i);
  		
      	if (temp == '1'){
          count++;
        }
    }
    System.out.println(count);
  }
} Main
import java.util.*;

public class Main{
  
  public static void main (String[] args){
  
  	Scanner scanner = new Scanner (System.in);
  
 	String number = scanner.nextLine();
    
  	int count = 0;
    
  	for (int i=0; i<3; i++){
  		char temp = number.charAt(i);
  		
      	if (temp == '1'){
          count++;
        }
    }
    System.out.println(count);
  }
}