import java.util.Scanner;
public class Main{
	public static void main(String[] args){
    	Scanner scan = new Scanner(System.in);
      	Integer a = scan.nextInt();
      	String s = a.toString();
      	int count = 0;
      	for(int i=0; i<s.length(); i++){
        	if(s.charAt(i) == '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);
      	Integer a = scan.nextInt();
      	String s = a.toString();
      	int count = 0;
      	for(int i=0; i<s.length(); i++){
        	if(s.charAt(i) == '1'){
            	count++;
            }
        }
      	System.out.println(count);
    }
} Main public static void main(String[] args){
    	Scanner scan = new Scanner(System.in);
      	Integer a = scan.nextInt();
      	String s = a.toString();
      	int count = 0;
      	for(int i=0; i<s.length(); i++){
        	if(s.charAt(i) == '1'){
            	count++;
            }
        }
      	System.out.println(count);
    } main {
    	Scanner scan = new Scanner(System.in);
      	Integer a = scan.nextInt();
      	String s = a.toString();
      	int count = 0;
      	for(int i=0; i<s.length(); i++){
        	if(s.charAt(i) == '1'){
            	count++;
            }
        }
      	System.out.println(count);
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) Integer a = scan.nextInt(); a scan.nextInt() scan.nextInt scan String s = a.toString(); s a.toString() a.toString a int count = 0; count 0 for(int i=0; i<s.length(); i++){
        	if(s.charAt(i) == '1'){
            	count++;
            }
        } int i=0; int i=0; i 0 i<s.length() i s.length() s.length s i++ i++ i {
        	if(s.charAt(i) == '1'){
            	count++;
            }
        } {
        	if(s.charAt(i) == '1'){
            	count++;
            }
        } if(s.charAt(i) == '1'){
            	count++;
            } s.charAt(i) == '1' s.charAt(i) s.charAt 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 scan = new Scanner(System.in);
      	Integer a = scan.nextInt();
      	String s = a.toString();
      	int count = 0;
      	for(int i=0; i<s.length(); i++){
        	if(s.charAt(i) == '1'){
            	count++;
            }
        }
      	System.out.println(count);
    }
} public class Main{
	public static void main(String[] args){
    	Scanner scan = new Scanner(System.in);
      	Integer a = scan.nextInt();
      	String s = a.toString();
      	int count = 0;
      	for(int i=0; i<s.length(); i++){
        	if(s.charAt(i) == '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);
      	Integer a = scan.nextInt();
      	String s = a.toString();
      	int count = 0;
      	for(int i=0; i<s.length(); i++){
        	if(s.charAt(i) == '1'){
            	count++;
            }
        }
      	System.out.println(count);
    }
}