import java.util.Scanner;

class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		sc.close();
		char c[] = s.toCharArray();
		int ans = 0;

		for (int i = 0; i < 3; i++)
			if (c[i] == '1')
				ans=ans+1;

		System.out.println(ans);

	}
} import java.util.Scanner; Scanner java.util class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		sc.close();
		char c[] = s.toCharArray();
		int ans = 0;

		for (int i = 0; i < 3; i++)
			if (c[i] == '1')
				ans=ans+1;

		System.out.println(ans);

	}
} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		sc.close();
		char c[] = s.toCharArray();
		int ans = 0;

		for (int i = 0; i < 3; i++)
			if (c[i] == '1')
				ans=ans+1;

		System.out.println(ans);

	} main {

		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		sc.close();
		char c[] = s.toCharArray();
		int ans = 0;

		for (int i = 0; i < 3; i++)
			if (c[i] == '1')
				ans=ans+1;

		System.out.println(ans);

	} 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 char c[] = s.toCharArray(); c s.toCharArray() s.toCharArray s int ans = 0; ans 0 for (int i = 0; i < 3; i++)
			if (c[i] == '1')
				ans=ans+1; int i = 0; int i = 0; i 0 i < 3 i 3 i++ i++ i if (c[i] == '1')
				ans=ans+1; if (c[i] == '1')
				ans=ans+1; c[i] == '1' c[i] c i '1' ans=ans+1 ans ans+1 ans 1 System.out.println(ans) System.out.println System.out System System.out ans String[] args args
import java.util.Scanner;

class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		sc.close();
		char c[] = s.toCharArray();
		int ans = 0;

		for (int i = 0; i < 3; i++)
			if (c[i] == '1')
				ans=ans+1;

		System.out.println(ans);

	}
}