import java.util.*;

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

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