import java.util.*;

public class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      	String str = sc.next();
      	int count = 0;
      	for(int i=0;i<str.length();i++){
        	char character = str.charAt(i);
          	if(character == '1'){
            	count++;
            }
        }
      System.out.print(count);
    }
} import java.util.*; util.* java public class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      	String str = sc.next();
      	int count = 0;
      	for(int i=0;i<str.length();i++){
        	char character = str.charAt(i);
          	if(character == '1'){
            	count++;
            }
        }
      System.out.print(count);
    }
} Main public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      	String str = sc.next();
      	int count = 0;
      	for(int i=0;i<str.length();i++){
        	char character = str.charAt(i);
          	if(character == '1'){
            	count++;
            }
        }
      System.out.print(count);
    } main {
    	Scanner sc = new Scanner(System.in);
      	String str = sc.next();
      	int count = 0;
      	for(int i=0;i<str.length();i++){
        	char character = str.charAt(i);
          	if(character == '1'){
            	count++;
            }
        }
      System.out.print(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String str = sc.next(); str sc.next() sc.next sc int count = 0; count 0 for(int i=0;i<str.length();i++){
        	char character = str.charAt(i);
          	if(character == '1'){
            	count++;
            }
        } int i=0; int i=0; i 0 i<str.length() i str.length() str.length str i++ i++ i {
        	char character = str.charAt(i);
          	if(character == '1'){
            	count++;
            }
        } {
        	char character = str.charAt(i);
          	if(character == '1'){
            	count++;
            }
        } char character = str.charAt(i); character str.charAt(i) str.charAt str i if(character == '1'){
            	count++;
            } character == '1' character '1' {
            	count++;
            } count++ count System.out.print(count) System.out.print 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 str = sc.next();
      	int count = 0;
      	for(int i=0;i<str.length();i++){
        	char character = str.charAt(i);
          	if(character == '1'){
            	count++;
            }
        }
      System.out.print(count);
    }
} public class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      	String str = sc.next();
      	int count = 0;
      	for(int i=0;i<str.length();i++){
        	char character = str.charAt(i);
          	if(character == '1'){
            	count++;
            }
        }
      System.out.print(count);
    }
} Main
import java.util.*;

public class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      	String str = sc.next();
      	int count = 0;
      	for(int i=0;i<str.length();i++){
        	char character = str.charAt(i);
          	if(character == '1'){
            	count++;
            }
        }
      System.out.print(count);
    }
}