

import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        java.util.Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int ans = 0;
        for (int i=0; i<3; i++){
            if (a % 10 == 1)
                ans++;
            a /= 10;
        }
        System.out.println(ans);
        }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        java.util.Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int ans = 0;
        for (int i=0; i<3; i++){
            if (a % 10 == 1)
                ans++;
            a /= 10;
        }
        System.out.println(ans);
        }
} Main public static void main(String[] args) throws Exception {
        java.util.Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int ans = 0;
        for (int i=0; i<3; i++){
            if (a % 10 == 1)
                ans++;
            a /= 10;
        }
        System.out.println(ans);
        } main {
        java.util.Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int ans = 0;
        for (int i=0; i<3; i++){
            if (a % 10 == 1)
                ans++;
            a /= 10;
        }
        System.out.println(ans);
        } java.util.Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int ans = 0; ans 0 for (int i=0; i<3; i++){
            if (a % 10 == 1)
                ans++;
            a /= 10;
        } int i=0; int i=0; i 0 i<3 i 3 i++ i++ i {
            if (a % 10 == 1)
                ans++;
            a /= 10;
        } {
            if (a % 10 == 1)
                ans++;
            a /= 10;
        } if (a % 10 == 1)
                ans++; a % 10 == 1 a % 10 a 10 1 ans++ ans a /= 10 a 10 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        java.util.Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int ans = 0;
        for (int i=0; i<3; i++){
            if (a % 10 == 1)
                ans++;
            a /= 10;
        }
        System.out.println(ans);
        }
} public class Main {
    public static void main(String[] args) throws Exception {
        java.util.Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int ans = 0;
        for (int i=0; i<3; i++){
            if (a % 10 == 1)
                ans++;
            a /= 10;
        }
        System.out.println(ans);
        }
} Main


import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        java.util.Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int ans = 0;
        for (int i=0; i<3; i++){
            if (a % 10 == 1)
                ans++;
            a /= 10;
        }
        System.out.println(ans);
        }
}