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