import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    
    String ss = sc.next();
    int count = 0;
    
    for (int i = 0; i <= 2; i++) {
      if (ss.charAt(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 ss = sc.next();
    int count = 0;
    
    for (int i = 0; i <= 2; i++) {
      if (ss.charAt(i) == '1') {
        count++;
      }
    }
    System.out.println(count);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    
    String ss = sc.next();
    int count = 0;
    
    for (int i = 0; i <= 2; i++) {
      if (ss.charAt(i) == '1') {
        count++;
      }
    }
    System.out.println(count);
  } main {
    Scanner sc = new Scanner(System.in);
    
    String ss = sc.next();
    int count = 0;
    
    for (int i = 0; i <= 2; i++) {
      if (ss.charAt(i) == '1') {
        count++;
      }
    }
    System.out.println(count);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String ss = sc.next(); ss sc.next() sc.next sc int count = 0; count 0 for (int i = 0; i <= 2; i++) {
      if (ss.charAt(i) == '1') {
        count++;
      }
    } int i = 0; int i = 0; i 0 i <= 2 i 2 i++ i++ i {
      if (ss.charAt(i) == '1') {
        count++;
      }
    } {
      if (ss.charAt(i) == '1') {
        count++;
      }
    } if (ss.charAt(i) == '1') {
        count++;
      } ss.charAt(i) == '1' ss.charAt(i) ss.charAt ss 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 ss = sc.next();
    int count = 0;
    
    for (int i = 0; i <= 2; i++) {
      if (ss.charAt(i) == '1') {
        count++;
      }
    }
    System.out.println(count);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    
    String ss = sc.next();
    int count = 0;
    
    for (int i = 0; i <= 2; i++) {
      if (ss.charAt(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 ss = sc.next();
    int count = 0;
    
    for (int i = 0; i <= 2; i++) {
      if (ss.charAt(i) == '1') {
        count++;
      }
    }
    System.out.println(count);
  }
}