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