import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String hundreds = sc.next();
		int count = 0;
		
		for(int i = 0; i < 3; i++) {
			if (hundreds.charAt(i) == '1') {
				count++;
			
			}
		}
		
		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 hundreds = sc.next();
		int count = 0;
		
		for(int i = 0; i < 3; i++) {
			if (hundreds.charAt(i) == '1') {
				count++;
			
			}
		}
		
		System.out.println(count);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String hundreds = sc.next();
		int count = 0;
		
		for(int i = 0; i < 3; i++) {
			if (hundreds.charAt(i) == '1') {
				count++;
			
			}
		}
		
		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);
		String hundreds = sc.next();
		int count = 0;
		
		for(int i = 0; i < 3; i++) {
			if (hundreds.charAt(i) == '1') {
				count++;
			
			}
		}
		
		System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String hundreds = sc.next(); hundreds sc.next() sc.next sc int count = 0; count 0 for(int i = 0; i < 3; i++) {
			if (hundreds.charAt(i) == '1') {
				count++;
			
			}
		} int i = 0; int i = 0; i 0 i < 3 i 3 i++ i++ i {
			if (hundreds.charAt(i) == '1') {
				count++;
			
			}
		} {
			if (hundreds.charAt(i) == '1') {
				count++;
			
			}
		} if (hundreds.charAt(i) == '1') {
				count++;
			
			} hundreds.charAt(i) == '1' hundreds.charAt(i) hundreds.charAt hundreds 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) {
		Scanner sc = new Scanner(System.in);
		String hundreds = sc.next();
		int count = 0;
		
		for(int i = 0; i < 3; i++) {
			if (hundreds.charAt(i) == '1') {
				count++;
			
			}
		}
		
		System.out.println(count);
	}

} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String hundreds = sc.next();
		int count = 0;
		
		for(int i = 0; i < 3; i++) {
			if (hundreds.charAt(i) == '1') {
				count++;
			
			}
		}
		
		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 hundreds = sc.next();
		int count = 0;
		
		for(int i = 0; i < 3; i++) {
			if (hundreds.charAt(i) == '1') {
				count++;
			
			}
		}
		
		System.out.println(count);
	}

}