import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		int count = 0;

		Scanner sc = new Scanner(System.in);

		String[] s = sc.next().split("");

		for(int i = 0; i < 3; i++) {
			if(s[i].equals("1")) {
				count++;
			}
		}

		System.out.println(count);
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

		int count = 0;

		Scanner sc = new Scanner(System.in);

		String[] s = sc.next().split("");

		for(int i = 0; i < 3; i++) {
			if(s[i].equals("1")) {
				count++;
			}
		}

		System.out.println(count);
	}
} Main public static void main(String[] args) {

		int count = 0;

		Scanner sc = new Scanner(System.in);

		String[] s = sc.next().split("");

		for(int i = 0; i < 3; i++) {
			if(s[i].equals("1")) {
				count++;
			}
		}

		System.out.println(count);
	} main {

		int count = 0;

		Scanner sc = new Scanner(System.in);

		String[] s = sc.next().split("");

		for(int i = 0; i < 3; i++) {
			if(s[i].equals("1")) {
				count++;
			}
		}

		System.out.println(count);
	} int count = 0; count 0 Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String[] s = sc.next().split(""); s sc.next().split("") sc.next().split sc.next() sc.next sc "" for(int i = 0; i < 3; i++) {
			if(s[i].equals("1")) {
				count++;
			}
		} int i = 0; int i = 0; i 0 i < 3 i 3 i++ i++ i {
			if(s[i].equals("1")) {
				count++;
			}
		} {
			if(s[i].equals("1")) {
				count++;
			}
		} if(s[i].equals("1")) {
				count++;
			} s[i].equals("1") s[i].equals s[i] s i "1" {
				count++;
			} count++ count 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) {

		int count = 0;

		Scanner sc = new Scanner(System.in);

		String[] s = sc.next().split("");

		for(int i = 0; i < 3; i++) {
			if(s[i].equals("1")) {
				count++;
			}
		}

		System.out.println(count);
	}
} public class Main {

	public static void main(String[] args) {

		int count = 0;

		Scanner sc = new Scanner(System.in);

		String[] s = sc.next().split("");

		for(int i = 0; i < 3; i++) {
			if(s[i].equals("1")) {
				count++;
			}
		}

		System.out.println(count);
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		int count = 0;

		Scanner sc = new Scanner(System.in);

		String[] s = sc.next().split("");

		for(int i = 0; i < 3; i++) {
			if(s[i].equals("1")) {
				count++;
			}
		}

		System.out.println(count);
	}
}