import java.util.*;
public class Main { 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
		int cnt = 0;
      	for(char c : str.toCharArray())
          if(c == '1') cnt++;
      	System.out.println(cnt);
        
    }
} 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 cnt = 0;
      	for(char c : str.toCharArray())
          if(c == '1') cnt++;
      	System.out.println(cnt);
        
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
		int cnt = 0;
      	for(char c : str.toCharArray())
          if(c == '1') cnt++;
      	System.out.println(cnt);
        
    } main {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
		int cnt = 0;
      	for(char c : str.toCharArray())
          if(c == '1') cnt++;
      	System.out.println(cnt);
        
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String str = sc.next(); str sc.next() sc.next sc int cnt = 0; cnt 0 for(char c : str.toCharArray())
          if(c == '1') cnt++; char c str.toCharArray() str.toCharArray str if(c == '1') cnt++; if(c == '1') cnt++; c == '1' c '1' cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args public class Main { 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
		int cnt = 0;
      	for(char c : str.toCharArray())
          if(c == '1') cnt++;
      	System.out.println(cnt);
        
    }
} public class Main { 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
		int cnt = 0;
      	for(char c : str.toCharArray())
          if(c == '1') cnt++;
      	System.out.println(cnt);
        
    }
} Main
import java.util.*;
public class Main { 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
		int cnt = 0;
      	for(char c : str.toCharArray())
          if(c == '1') cnt++;
      	System.out.println(cnt);
        
    }
}