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