import java.util.*;
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    int ans = 0;
    for (int i = 0; i < 3; i++){
      if (s.charAt(i) == '1'){ans += 1;}
    }
    System.out.println(ans);
  }
} import java.util.*; util.* java class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    int ans = 0;
    for (int i = 0; i < 3; i++){
      if (s.charAt(i) == '1'){ans += 1;}
    }
    System.out.println(ans);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    int ans = 0;
    for (int i = 0; i < 3; i++){
      if (s.charAt(i) == '1'){ans += 1;}
    }
    System.out.println(ans);
  } main {
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    int ans = 0;
    for (int i = 0; i < 3; i++){
      if (s.charAt(i) == '1'){ans += 1;}
    }
    System.out.println(ans);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.next(); s sc.next() sc.next sc int ans = 0; ans 0 for (int i = 0; i < 3; i++){
      if (s.charAt(i) == '1'){ans += 1;}
    } int i = 0; int i = 0; i 0 i < 3 i 3 i++ i++ i {
      if (s.charAt(i) == '1'){ans += 1;}
    } {
      if (s.charAt(i) == '1'){ans += 1;}
    } if (s.charAt(i) == '1'){ans += 1;} s.charAt(i) == '1' s.charAt(i) s.charAt s i '1' {ans += 1;} ans += 1 ans 1 System.out.println(ans) System.out.println System.out System System.out ans String[] args args
import java.util.*;
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    int ans = 0;
    for (int i = 0; i < 3; i++){
      if (s.charAt(i) == '1'){ans += 1;}
    }
    System.out.println(ans);
  }
}
