import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split("");
		sc.close();
		int cnt = 0;

		for(int i = 0; i< line.length; i++) {
			if(line[i].equals("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[] line = sc.nextLine().split("");
		sc.close();
		int cnt = 0;

		for(int i = 0; i< line.length; i++) {
			if(line[i].equals("1")) {
				cnt++;
			}
		}

		System.out.println(cnt);

	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split("");
		sc.close();
		int cnt = 0;

		for(int i = 0; i< line.length; i++) {
			if(line[i].equals("1")) {
				cnt++;
			}
		}

		System.out.println(cnt);

	} main {
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split("");
		sc.close();
		int cnt = 0;

		for(int i = 0; i< line.length; i++) {
			if(line[i].equals("1")) {
				cnt++;
			}
		}

		System.out.println(cnt);

	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String[] line = sc.nextLine().split(""); line sc.nextLine().split("") sc.nextLine().split sc.nextLine() sc.nextLine sc "" sc.close() sc.close sc int cnt = 0; cnt 0 for(int i = 0; i< line.length; i++) {
			if(line[i].equals("1")) {
				cnt++;
			}
		} int i = 0; int i = 0; i 0 i< line.length i line.length line line.length i++ i++ i {
			if(line[i].equals("1")) {
				cnt++;
			}
		} {
			if(line[i].equals("1")) {
				cnt++;
			}
		} if(line[i].equals("1")) {
				cnt++;
			} line[i].equals("1") line[i].equals line[i] line i "1" {
				cnt++;
			} 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[] line = sc.nextLine().split("");
		sc.close();
		int cnt = 0;

		for(int i = 0; i< line.length; i++) {
			if(line[i].equals("1")) {
				cnt++;
			}
		}

		System.out.println(cnt);

	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split("");
		sc.close();
		int cnt = 0;

		for(int i = 0; i< line.length; i++) {
			if(line[i].equals("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[] line = sc.nextLine().split("");
		sc.close();
		int cnt = 0;

		for(int i = 0; i< line.length; i++) {
			if(line[i].equals("1")) {
				cnt++;
			}
		}

		System.out.println(cnt);

	}

}
