import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String str = sc.next();
		sc.close();
		char[] si = str.toCharArray();
		int count = 0;

		for (int i = 0; i < si.length; i++) {
			if(si[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 str = sc.next();
		sc.close();
		char[] si = str.toCharArray();
		int count = 0;

		for (int i = 0; i < si.length; i++) {
			if(si[i]== '1') {
				count++;
			}
		}

		System.out.println(count);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String str = sc.next();
		sc.close();
		char[] si = str.toCharArray();
		int count = 0;

		for (int i = 0; i < si.length; i++) {
			if(si[i]== '1') {
				count++;
			}
		}

		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);
		String str = sc.next();
		sc.close();
		char[] si = str.toCharArray();
		int count = 0;

		for (int i = 0; i < si.length; i++) {
			if(si[i]== '1') {
				count++;
			}
		}

		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 sc.close() sc.close sc char[] si = str.toCharArray(); si str.toCharArray() str.toCharArray str int count = 0; count 0 for (int i = 0; i < si.length; i++) {
			if(si[i]== '1') {
				count++;
			}
		} int i = 0; int i = 0; i 0 i < si.length i si.length si si.length i++ i++ i {
			if(si[i]== '1') {
				count++;
			}
		} {
			if(si[i]== '1') {
				count++;
			}
		} if(si[i]== '1') {
				count++;
			} si[i]== '1' si[i] si 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 str = sc.next();
		sc.close();
		char[] si = str.toCharArray();
		int count = 0;

		for (int i = 0; i < si.length; i++) {
			if(si[i]== '1') {
				count++;
			}
		}

		System.out.println(count);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String str = sc.next();
		sc.close();
		char[] si = str.toCharArray();
		int count = 0;

		for (int i = 0; i < si.length; i++) {
			if(si[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 str = sc.next();
		sc.close();
		char[] si = str.toCharArray();
		int count = 0;

		for (int i = 0; i < si.length; i++) {
			if(si[i]== '1') {
				count++;
			}
		}

		System.out.println(count);
	}

}
