import java.util.Scanner;

public class Main {

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

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

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

public class Main {

	public static void main(String[] args) {
	Scanner sc = new Scanner(System.in);
	String S = sc.next();
	sc.close();
	
	int cnt = 0;
	for(int i=0;i<3;i++)if (S.charAt(i)=='1') cnt++;
	System.out.println(cnt);
	
	}
}
