
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int cnt = 0;
		while(true) {
			if(n % 10 == 1)cnt++;
			n /= 10;
			if(n == 0) break;
		}
		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);
		int n = sc.nextInt();
		int cnt = 0;
		while(true) {
			if(n % 10 == 1)cnt++;
			n /= 10;
			if(n == 0) break;
		}
		System.out.println(cnt);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int cnt = 0;
		while(true) {
			if(n % 10 == 1)cnt++;
			n /= 10;
			if(n == 0) break;
		}
		System.out.println(cnt);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int cnt = 0;
		while(true) {
			if(n % 10 == 1)cnt++;
			n /= 10;
			if(n == 0) break;
		}
		System.out.println(cnt);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int cnt = 0; cnt 0 while(true) {
			if(n % 10 == 1)cnt++;
			n /= 10;
			if(n == 0) break;
		} true {
			if(n % 10 == 1)cnt++;
			n /= 10;
			if(n == 0) break;
		} if(n % 10 == 1)cnt++; n % 10 == 1 n % 10 n 10 1 cnt++ cnt n /= 10 n 10 if(n == 0) break; n == 0 n 0 break; 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);
		int n = sc.nextInt();
		int cnt = 0;
		while(true) {
			if(n % 10 == 1)cnt++;
			n /= 10;
			if(n == 0) break;
		}
		System.out.println(cnt);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int cnt = 0;
		while(true) {
			if(n % 10 == 1)cnt++;
			n /= 10;
			if(n == 0) break;
		}
		System.out.println(cnt);
	}

} Main

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int cnt = 0;
		while(true) {
			if(n % 10 == 1)cnt++;
			n /= 10;
			if(n == 0) break;
		}
		System.out.println(cnt);
	}

}
