import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		String str = sc.next();
		int count = 0;

		for (int i = 0; i < str.length(); i++) {
			count += str.charAt(i) == '1' ? 1 : 0;
		}

		System.out.println(count);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		String str = sc.next();
		int count = 0;

		for (int i = 0; i < str.length(); i++) {
			count += str.charAt(i) == '1' ? 1 : 0;
		}

		System.out.println(count);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		String str = sc.next();
		int count = 0;

		for (int i = 0; i < str.length(); i++) {
			count += str.charAt(i) == '1' ? 1 : 0;
		}

		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);

		String str = sc.next();
		int count = 0;

		for (int i = 0; i < str.length(); i++) {
			count += str.charAt(i) == '1' ? 1 : 0;
		}

		System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String str = sc.next(); str sc.next() sc.next sc int count = 0; count 0 for (int i = 0; i < str.length(); i++) {
			count += str.charAt(i) == '1' ? 1 : 0;
		} int i = 0; int i = 0; i 0 i < str.length() i str.length() str.length str i++ i++ i {
			count += str.charAt(i) == '1' ? 1 : 0;
		} {
			count += str.charAt(i) == '1' ? 1 : 0;
		} count += str.charAt(i) == '1' ? 1 : 0 count str.charAt(i) == '1' ? 1 : 0 str.charAt(i) == '1' str.charAt(i) str.charAt str i '1' 1 0 System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		String str = sc.next();
		int count = 0;

		for (int i = 0; i < str.length(); i++) {
			count += str.charAt(i) == '1' ? 1 : 0;
		}

		System.out.println(count);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		String str = sc.next();
		int count = 0;

		for (int i = 0; i < str.length(); i++) {
			count += str.charAt(i) == '1' ? 1 : 0;
		}

		System.out.println(count);
	}
} Main
import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		String str = sc.next();
		int count = 0;

		for (int i = 0; i < str.length(); i++) {
			count += str.charAt(i) == '1' ? 1 : 0;
		}

		System.out.println(count);
	}
}