import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		  Scanner in = new Scanner(System.in);
		  String s = in.next();
		  int count = 0;

		if ( s.charAt(0) == '1') {
			count++;
		}
		if( s.charAt(1) == '1') {
			count++;
		}
		if( s.charAt(2) == '1') {
			count++;
		}
		System.out.println(count);
		in.close();
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args){
		  Scanner in = new Scanner(System.in);
		  String s = in.next();
		  int count = 0;

		if ( s.charAt(0) == '1') {
			count++;
		}
		if( s.charAt(1) == '1') {
			count++;
		}
		if( s.charAt(2) == '1') {
			count++;
		}
		System.out.println(count);
		in.close();
	}
} Main public static void main(String[] args){
		  Scanner in = new Scanner(System.in);
		  String s = in.next();
		  int count = 0;

		if ( s.charAt(0) == '1') {
			count++;
		}
		if( s.charAt(1) == '1') {
			count++;
		}
		if( s.charAt(2) == '1') {
			count++;
		}
		System.out.println(count);
		in.close();
	} main {
		  Scanner in = new Scanner(System.in);
		  String s = in.next();
		  int count = 0;

		if ( s.charAt(0) == '1') {
			count++;
		}
		if( s.charAt(1) == '1') {
			count++;
		}
		if( s.charAt(2) == '1') {
			count++;
		}
		System.out.println(count);
		in.close();
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) String s = in.next(); s in.next() in.next in int count = 0; count 0 if ( s.charAt(0) == '1') {
			count++;
		} s.charAt(0) == '1' s.charAt(0) s.charAt s 0 '1' {
			count++;
		} count++ count if( s.charAt(1) == '1') {
			count++;
		} s.charAt(1) == '1' s.charAt(1) s.charAt s 1 '1' {
			count++;
		} count++ count if( s.charAt(2) == '1') {
			count++;
		} s.charAt(2) == '1' s.charAt(2) s.charAt s 2 '1' {
			count++;
		} count++ count System.out.println(count) System.out.println System.out System System.out count in.close() in.close in String[] args args public class Main {
	public static void main(String[] args){
		  Scanner in = new Scanner(System.in);
		  String s = in.next();
		  int count = 0;

		if ( s.charAt(0) == '1') {
			count++;
		}
		if( s.charAt(1) == '1') {
			count++;
		}
		if( s.charAt(2) == '1') {
			count++;
		}
		System.out.println(count);
		in.close();
	}
} public class Main {
	public static void main(String[] args){
		  Scanner in = new Scanner(System.in);
		  String s = in.next();
		  int count = 0;

		if ( s.charAt(0) == '1') {
			count++;
		}
		if( s.charAt(1) == '1') {
			count++;
		}
		if( s.charAt(2) == '1') {
			count++;
		}
		System.out.println(count);
		in.close();
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		  Scanner in = new Scanner(System.in);
		  String s = in.next();
		  int count = 0;

		if ( s.charAt(0) == '1') {
			count++;
		}
		if( s.charAt(1) == '1') {
			count++;
		}
		if( s.charAt(2) == '1') {
			count++;
		}
		System.out.println(count);
		in.close();
	}
}
