import java.util.*;

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

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