import java.util.*;
public class Main {
	public static void main(String args[]) {
    	Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
       	int cnt = 0;
        if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	System.out.println(cnt);
	}
}
        
         import java.util.*; util.* java public class Main {
	public static void main(String args[]) {
    	Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
       	int cnt = 0;
        if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	System.out.println(cnt);
	}
} Main public static void main(String args[]) {
    	Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
       	int cnt = 0;
        if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	System.out.println(cnt);
	} main {
    	Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
       	int cnt = 0;
        if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	System.out.println(cnt);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int cnt = 0; cnt 0 if(a % 10 == 1) cnt++; a % 10 == 1 a % 10 a 10 1 cnt++ cnt a /= 10 a 10 if(a % 10 == 1) cnt++; a % 10 == 1 a % 10 a 10 1 cnt++ cnt a /= 10 a 10 if(a % 10 == 1) cnt++; a % 10 == 1 a % 10 a 10 1 cnt++ cnt 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 a = sc.nextInt();
       	int cnt = 0;
        if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	System.out.println(cnt);
	}
} public class Main {
	public static void main(String args[]) {
    	Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
       	int cnt = 0;
        if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	System.out.println(cnt);
	}
} Main
import java.util.*;
public class Main {
	public static void main(String args[]) {
    	Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
       	int cnt = 0;
        if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	a /= 10;
      	if(a % 10 == 1) cnt++;
      	System.out.println(cnt);
	}
}
        
        