import java.util.*;

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