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;
		int n = s.length();
		for (int i = 0; i < n; ++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;
		int n = s.length();
		for (int i = 0; i < n; ++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;
		int n = s.length();
		for (int i = 0; i < n; ++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;
		int n = s.length();
		for (int i = 0; i < n; ++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 int n = s.length(); n s.length() s.length s for (int i = 0; i < n; ++i) {
			if (s.charAt(i) == '1')
				++cnt;
		} int i = 0; int i = 0; i 0 i < n i n ++i ++i i {
			if (s.charAt(i) == '1')
				++cnt;
		} {
			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;
		int n = s.length();
		for (int i = 0; i < n; ++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;
		int n = s.length();
		for (int i = 0; i < n; ++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;
		int n = s.length();
		for (int i = 0; i < n; ++i) {
			if (s.charAt(i) == '1')
				++cnt;
		}

		System.out.println(cnt);
	}

}
