import java.util.*;

public class Main {
  public static void main(String[] args) {
          Scanner sc = new Scanner(System.in);
          int num = sc.nextInt();
    	  int count = 0;
          List<Integer> list = new ArrayList<>();
          while (num > 0){
              list.add(num % 10);
              num /= 10;
            }
          for(int a : list) {
            if(a == 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);
          int num = sc.nextInt();
    	  int count = 0;
          List<Integer> list = new ArrayList<>();
          while (num > 0){
              list.add(num % 10);
              num /= 10;
            }
          for(int a : list) {
            if(a == 1){
              count++;
        }
          }
            System.out.println(count);
          }
    } Main public static void main(String[] args) {
          Scanner sc = new Scanner(System.in);
          int num = sc.nextInt();
    	  int count = 0;
          List<Integer> list = new ArrayList<>();
          while (num > 0){
              list.add(num % 10);
              num /= 10;
            }
          for(int a : list) {
            if(a == 1){
              count++;
        }
          }
            System.out.println(count);
          } main {
          Scanner sc = new Scanner(System.in);
          int num = sc.nextInt();
    	  int count = 0;
          List<Integer> list = new ArrayList<>();
          while (num > 0){
              list.add(num % 10);
              num /= 10;
            }
          for(int a : list) {
            if(a == 1){
              count++;
        }
          }
            System.out.println(count);
          } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int num = sc.nextInt(); num sc.nextInt() sc.nextInt sc int count = 0; count 0 List<Integer> list = new ArrayList<>(); list new ArrayList<>() while (num > 0){
              list.add(num % 10);
              num /= 10;
            } num > 0 num 0 {
              list.add(num % 10);
              num /= 10;
            } list.add(num % 10) list.add list num % 10 num 10 num /= 10 num 10 for(int a : list) {
            if(a == 1){
              count++;
        }
          } int a list {
            if(a == 1){
              count++;
        }
          } {
            if(a == 1){
              count++;
        }
          } if(a == 1){
              count++;
        } a == 1 a 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);
          int num = sc.nextInt();
    	  int count = 0;
          List<Integer> list = new ArrayList<>();
          while (num > 0){
              list.add(num % 10);
              num /= 10;
            }
          for(int a : list) {
            if(a == 1){
              count++;
        }
          }
            System.out.println(count);
          }
    } public class Main {
  public static void main(String[] args) {
          Scanner sc = new Scanner(System.in);
          int num = sc.nextInt();
    	  int count = 0;
          List<Integer> list = new ArrayList<>();
          while (num > 0){
              list.add(num % 10);
              num /= 10;
            }
          for(int a : list) {
            if(a == 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);
          int num = sc.nextInt();
    	  int count = 0;
          List<Integer> list = new ArrayList<>();
          while (num > 0){
              list.add(num % 10);
              num /= 10;
            }
          for(int a : list) {
            if(a == 1){
              count++;
        }
          }
            System.out.println(count);
          }
    }